I'm flattered - read under Garland's entry, "Ascended Meme".
http://tvtropes.org/pmwiki/pmwiki.php/Characters/ptitletxoa94kz
Second time TV Tropes has mentioned me ;p
On the subject of villains:
FF1 - no one really to include.
FF2 - Leon would work, if they could think of a fighting style
FF3 - Xande, durr hurr
FF4 - No one really, can't have just one Archfiend over the other three in, and compared to Kain there's no way Zemus deserves to get in.
FF5 - GILGAMESH.
FF6 - Unless you wanna get wacky with like, Ultros or Gestahl, I say have Celes in as a villain character in the vein of Golbez and Jecht - on Chaos' side but not truly evil, acting to help the heroes in her own way while serving Chaos.
FF7 - Well there's Rufus and the Turks. I would say no one from the spin-offs though, there's Weiss and Genesis sure but let's stick to the original I say. But no secondary FF7 villain deserved to get in over Tifa.
FF8 - Seifer plzkthxbai, though Laguna was a nice and unexpected choice.
FF9 - No one, Garland and Brahne wouldn't work, and who else is left then?
FF10 - Seymour, durrrrr. But Seymour over Yuna? People would bitch.
FF11 - Eald'narche would have been much better over Prishe.
So yeah, they had options, the problem was they were looking at excluding hero characters who would work better. Still, Eald'narche, Celes and Xande would all have made excellent additions to Team Chaos without sacrificing one of the new heroes. Save for Prishe, but meh.
Also, including Eald'narche would let them have the Celestial Nexus as the FF11 arena, and it looks like a far more interesting place for a Dissidia match to take place in than the place they included.