What I said was a direct quote from his Ultimania interview. Taken a little out of context, perhaps, but still...

Nomura: If we stick exactly to final bosses, we’d get characters such as FFX’s Yu Yevon. Characters who it would be difficult to give much personality to, or whose design doesn’t fit in with a fighting game. So I thought that it would be better to take characters with a rivalry, or with strong connections. Also, I personally really wanted to have Kain in the game. Originally we planned to have about 5 hidden characters, and even as that number started to shrink, Kain remained a candidate right to the end. When it was finally decided to cut him I said, “for FFIV’s Chaos character wouldn’t Kain and not Golbez be fine?” But we had to think of the balance with the other titles, and he was cut.
And from later in the interview...

Nomura: Well, if we did a sequel I think Kain is definitely in (laughs). I’ve got a lot of interesting ideas, but as far as the situation goes actually going ahead with the project would be tricky… If there were enough demand for a Dissidia II, the situation might change, so I think I’d like to rethink it at that time.
So, yeah. Maybe the first one was all main characters, but I highly doubt a sequel would be. For one thing, there are tons of supporting characters who have massive fanbases to capitalize on. For another, how else would you justify a sequel? I mean, you would be adding, what, four new characters? Six at a maximum (and that would be if they wanted to release character info of FFXIV, which is unlikely). Sorry, but no. To do a sequel, they would have to add in more characters, and that pretty much guarantees delving into the support characters. Ideally, we'd be looking at one support hero/villain per game, which would give us...

-Red Mage / Astos or Bikke
-Minwu ('cause he rocks, even though it would probably go to Maria) / Um, yeah, can't think of any real good option here.
-Summoner (or any other job change, I picked this one because it should have fairly unique gameplay) / Xande
-Rosa (sorry, Tellah, but she'd be the obvious one, due to relationship with Kain) / Kain
-Faris (don't want too many healer/cleric sidekicks, which is why no Lenna) / Gilgamesh (win)
-Locke or Setzer, would be my guess (thief or chance based gameplay) / Gesthal
-Tifa (fun combo-based brawler) / Rufus (perhaps you only fight him once, but he is the other recurring villain here, especially since there's no way you could separate Reno and Rude)
-Rinoa / Seifer
-Garnet (summoner gameplay again) / Haven't played enough to choose a good secondary villain. I know, shame on me.
-Auron / Seymour (hate his guts, but, again, limited options)
-Pick a few, I'm probably never going to play this
-Balthier and Fran (no hero from XII in Dissidia, so two for the sequel) / Vayne
-Lightning / Villain


Although I suppose we could cheat a little...

Ramza / Delita (I always think of that psycho as the villain, but you can pick another)
Marche / Llednar (or Remedi, if she was done well enough)
Luso / Illua
Sora / Ansem
Chrono / Magus