Rinoa

[Vost]

Your theory has little to back it up I'm afraid. Their is no reference at all in the game itslef, of an alternate timeline that Ultemacia hails from in the story. No mention of any parallel time lines. In fact, Ellone makes it a point to explain that she learned that you cannot alter time. All her attempts only made the the events she wished to change come true. VIII's view of time and time travel for lack of any better explanation given by the story, the Ultimania, or even Square itself points to the fact that time is linear and unchangeable in the VIII Mythos.

The fact that Squall and SeeD's actions lead to Ultemacia giving her powers away and thus allowing her the ability to travel to this time period, due to actually having something connecting her to it. Her powers.

Ultemacia has very little back story but the best theory I've heard concerning her motive is that due to the public spectacle of the wars Adel and Edea brought in the past, the general public in her time may have hunted Sorceress' out of fear of history repeating itself. Thus coming from a future where she was hunted and hated for no reason, she lost her mind and decided the world was her enemy. Regretfully, this theory cannot explain how Ultemacia learned about Time Compression but that whole nonsense has always been ill defined in the game.

The very nature of Time Compression does not necessarily mean that time is being altered, only that it is being compressed into one temporal singularity. Therefore, my theory can still hold next to the idea that the past cannot be changed. This is because it is no longer the 'past' or 'present' or 'future' per se, but rather ONE time. It is THIS one time that is changed, not the specific past or specific present or specific future that at one time was separate from it.

Your theory on Ultimecia's motivation is ridiculously weak. Mine ties the plot and explains her obsessions cogently. There is a lot of in game evidence to support this theory but I will not get into this here because it has already been mentioned in many other R=U posts.