Zylos, any pics online from that poster?
Seems like Dissidia will feature 2 characters from each FF series, 1 hero, 1 villain.
So, the possible lineup for the game could be this one:
Warrior of Light / Garland (Confirmed)
Firion / Borghen (Possible lineup)
Onion Knight or Luneth or Refia (since there's few female characters, Refia from the remake is most likely to appear) / Dark Warrior (referred in the background story)
Cecil (Or paladin Cecil) / Golbez (Most likely)
Bartz / Gilgamesh (Gilgamesh better appear or else i'm gonna be pissed.) Or X-Death
Terra / Kefka
Cloud / Sephiroth (Sephiroth Confirmed)
Squall / Seifer (Most likely to be lined up like this, since Ultimecia is way too overrated.)
Zidane / Kuja (Confirmed)
Yuna or Tidus / Seymour or Jecht (Another possible lineup)
Vaan or Basch OR Asche / Vayne Solidor
Lightning (FFXIII) /
(No Boss yet known)
This is just speculation, but if the lineup gets to be this big, they could at least make the game more interesting by adding DQ characters or even Mana characters, since these were spawned FROM FF.