You've raised some interesting possibilities, Throne, although I'm afraid I disagree with some of them. I don't have time for an extensive analysis of Kabballist elements in FFV at the moment, though I will comment on your assessment of Neo Ex-Death at the end.

While I'm glad that someone else recognizes that Neo Ex-Death is not simply a different or evolved version of Ex-Death, Enuo is not the most likely identity for the entity. Your first suggestion is by far the closest, as Neo Ex-Death is the very embodiment of the Void. I will also show that the similarities to Necron are much more profound than they may immediately appear. I'll begin by examining the very dialogue you cited.

Neo-Exdeath: I am Neo-Exdeath! I shall erase all memory, all existence, all
dimensions. Then I too, shall disappear for, eternity!
Enuo, as suggested by the game, sought ascension, not negation. For Enuo, the Void was a means to potentially unlimited power. For him, harnessing the Void could very well lead to a sort of artificial apotheosis; he was, however, defeated. Neo Ex-Death, the entity at the end of the game, seeks to negate all existence (as well as all memory, which I will address momentarily. Most importantly, Neo Ex-Death claims that it too will disappear for eternity. While its possible that Enuo could have been warped to the point where he sought physical and spirtitual oblivion even for himself, it makes more sense that a concept that in essence is negation would seek even to forever banish itself.

Also, remember Ex-Death's fate before the final battle.

*The void begins to consume X-Death*

Exdeath: WHY? I had the power of the Void! What is Void? Arrrgh!
Ex-Death questions the actual nature of the Void. The Void, for its part, consumes Ex-Death, just as it seeks to consume everything. Ex-Death questions the Void since it is absorbing him; the terrible reality of pure, all-encompassing negation is certainly a horrible fate. While Enuo could, arguably, have manipulated the Void to eliminate Ex-Death, these lines seem far more indicative of the Void simply following its own imperative.

The Enuo argument also overlooks that crucial passage explicating the war against Enuo. It is stated that he was defeated, but that the Void remained.

Eventually, using the 12 Legendary Weapons, the people defeated Enuo. But
they were not able to get rid of the Void that Enuo had created.
One could suggest that Enuo was merely banished, although that seems imprudent (to say the least), given what Enuo had demonstrated he was capable of doing. In any case, however, it is stated that he was defeated, but that the Void remained (which suggests, to me, an understanding that the Void was at this point a far greater threat).

Finally, if the entity at the end of the game was Enuo, it would have been no great task to call it "Enuo." True, it could have been called the Void, but Neo Ex-Death as a name retains the idea that Ex-Death himself had been absorbed.

To truly confirm this point, however, I feel it is necessary to look to FFIX, which closely mirrors FFV on a number of levels. Here are some ideas I developed concerning FFIX, which will help us take a closer look at FFV.

The following is taken from my thread "FFIX and the Implicit Reference."

Quote Originally Posted by masamune1600
[...]Thus, as long as evil is perpetuated, so is the potential for Necron to see reason to perform his nullifying work.

Furthermore, in saying "nullifying", I suggest that Necron's purpose was more than to kill, to turn life to death. Rather, Necron sought something more profound and more horrible: the negation, the very dissolution of existence as we understand it.

(Necron): "I exist for one purpose..."
"To return everything back to the zero world, where there is no life and no crystal to give life."
"In a world of nothing, fear does not exist. This is the world that all life desires."
Necron, according to the dialogue, desires to return "everything" to the "zero world." Not only is this zero world a place with no life, it is also a place with no crystal. If the crystal, which gives life, disappears, then theoretically even the possibility of life also vanishes. Also, the crystal deals heavily with the idea of memory.

Voice of Garland: You have entered a new realm. There are no more
words. There is no more space... Follow your memory, and march forth...

Zidane: Garland, what exactly is our memory!?

Voice of Garland: .........

Zidane: Why can I remember other people's experiences and events that
happened before my time?

Voice of Garland: .........

Zidane: Garland, please! Tell me!

Voice of Garland: ...Do not limit memory to just one individual's
experiences from birth. That is only the surface. Every life born into
this world, whether natural or artificial, requires a parent. And that
parent also requires a parent. Life is connected, one to another... If
you trace the root of all life, there exists one source. The same can
be said for memory. All life constitutes an intelligence that holds
memory beyond experience. Memory is not isolated within individuals. It
is an accumulation of generations of memories that continues to evolve.
You can say that memory and evolution go hand in hand. But most life-
forms do not understand the true nature of memories... ...which explains
why most memories never cross paths.

Zidane: ...So, what am I gonna find by tracing back our roots?

Voice of Garland: ...A presence that presides over all life and memories.
The crystal...

Zidane: Crystal...
As noted in a previous post, it's possible that the zero world doesn't necessarily imply total negation. However, it is a possibility. What's really relevant, however, is this: the idea bears striking similarity to a previous FF concept. Note that I managed to sneak in the word "voids." Clearly, negation and nothingness are not new concepts to the series. Neo Ex-Death, the final boss of FFV, is the very embodiment of the Void. Similarly, Necron can be interpreted as the embodiment, or more accurately the will, of negation. However, even if you find these ideas difficult to accept, the fact remains that Necron bears a clear resemblance to Neo Ex-Death.

Furthermore, "Necron" was not the original name for this entity. The Japanese version of the game calls it the "Darkness of Eternity", which still appears in the dialogue.

Zidane: U-Ugh... What happened to the crystal...? ...Where is this?

Unknown Voice: You stand before the final dimension, and I am the
darkness of eternity...

Zidane: Wh-Who are you!?
Necron, the Darkness of Eternity, is just that. He is the force that would remove the light, the crystal, from existence. And who's to say that, at least in theory, the crystal is not responsible for time? If the crystal disappears, taking with it time, then the darkness of eternity (you can, for fun, compare this to Chrono Cross' Darkness Beyond Time if you like) becomes a chilling reality. Neo Ex-Death, should it prevail against Bartz and company, would seem to signify the victory of the Void over that which currently exists. The Void is a plot device, and can be interpreted in different ways, but I don't think it's too great a stretch to compare the darkness of eternity idea.

Throughout this post, I've constructed a view of Necron as a force to essentially dissolve existence.[...]
I again examined FFV later in the thread.

Quote Originally Posted by masamune1600
First, I'll return to Necron. While I still see implicit reference to Zeromus, that seems to be a secondary link. The reference to Neo Ex-Death already seemed stronger, and a couple new points of information add further support to the implicit recollection of Neo Ex-Death. The first is obvious: Grand Cross. This spell, first seen used by Neo Ex-Death in FFV, is arguably Necron's most feared attack. In both cases, Grand Cross can inflict a host of extremely debilitating status effects. This is not a move that is very common in the series, and I believe that Necron had a technique of this name primarily for the purpose of recalling Neo Ex-Death.

The second new link is much more subtle. We know that, preceding Neo Ex-Death (as stated before, the embodiment of the Void), Bartz and company fought it out with Ex-Death. After this fight is finished up, Ex-Death is absorbed into the Void. We see somewhat of a similar situation in FFIX. Like Ex-Death, Kuja seemed a lock to be the final boss, as he (again, like Ex-Death) was the party's primary enemy heading to the final showdown. Also, like Ex-Death, Kuja is essentially doomed following his final confrontation with the heroes. Although Kuja blasts Zidane and company with Ultima (what exactly happened to the heroes as a result of Ultima is currently being debated, but is irrelevant to this topic), he falls (literally) following the fight. His time, like Ex-Death's, is up. Nevertheless, the game is not over: a new presence, alluded to if never actually stated, arises to confront the party. At stake in this final battle is existence as we know it: Neo Ex-Death seeks the perpetual nothingness of the Void, while Necron literally states a desire to return everything to the "zero world."

This idea, then, serves two purposes: we see yet another link between Neo Ex-Death and Necron, while also establishing an implicit reference to Ex-Death in the person of Kuja.

At this time, I would like to remind anyone reading this thread that the stories of FFIX and FFV were immensely different. I feel that the above links, and the one I am about to address, were intentionally included to recall the FFV experience, but not to copy the game due to failing inspiration.

There does not seem to be a great deal of analysis concerning FFV, perhaps because the game was initially only released in Japan. However, yet another striking similarity between FFV and FFIX exists: the idea of multiple worlds. In FFV, Ex-Death is sealed; he is trapped by crystals in a world other than is own. However, even sealed, Ex-Death is able to manipulate circumstances so that the crystals are shattered and he is freed. This leads the characters to journey to the second world, where Ex-Death returns. Similarly, the characters in FFIX find it necessary to journey to a second world, Terra, where Kuja and Garland have returned. We learn in FFIX that Garland seeks to assimilate Gaia into Terra; this is strangely reminiscent of FFV, where the worlds eventually do merge (creating a third map, that has transplanted locations from both). Ultimately, however, both the third world of FFV and (depending on your interpretation of FFIX) are threatened by the Void, or a Void-like concept. Thus, while the Gaia/Terra plot intricacies of FFIX are fascinating in their own right, they may also implicitly reference a similar (though, admittedly nowhere near exact) story element in FFV....
I've included all of my FFV/FFIX analysis in the document for your convenience. The reason I've done so, however, deals with the similarities between Neo Ex-Death and Necron (the Darkness of Eternity, really, which ironically describes the Void rather accurately as well). Necron is a force whose origins are debated (some suggest Necron is a cosmic entity that has always existed, others say that Necron may have been created by Garland). This, then, closely mirrors the confusion in the script regarding the Void (this may even have been an obscure joke thrown in FFIX by Square). We see, ultimately, that Necron, the very force that could "void" everything, must be defeated. So it is in FFV.

Also note that, in the dialogue we've both cited, Neo Ex-Death seeks to negate memory. Memory is very important, although it may seem strange that it is mentioned in the same way as all of existence. However, referring to my segment on Necron seeking to undo memory by undoing the Crystal, we get a glimpse into the real significance of what was happening. The point, however, remains, that the implicit responsibility of Necron helps us see Neo Ex-Death as what it really is: the manifestation of the Void.

While I won't go so far as to fully endorse this idea, I think it's possible that Ex-Death himself was actually a reincarnation or evolution of Enuo. Enuo could possibly, after all, have bound himself to the tree, or otherwise created a new darkness.

In any case, Throne, excellent job with your appraisal, even if I don't agree with everything. I'll be back later to examine the Tree of Life concept, but, for now, thanks for calling attention to an unfairly underrated story and an unjustly ignored game.