According to Siliconera. ( http://www.siliconera.com/2012/02/29/gilgamesh-and
Gilgamesh (FF V version) & an unknown villain from VI (Kefka most likely) & Jhil from XIII.
It won't be Kefka they'll more than likely use a character who isn't essiential to plot so it'll be Ultros. Wonder if they give Gilgamesh a voice which will it be XII or Dissidia I hope for XII John DiMaggio ftw.
Two monsters from VI now, apparently. First of which is apparently the most annoying monster from VI, Chupon/Typhon.
With that in mind, I wouldn't be surprising to see the second one being Ultros.
Jhil is to release next week, and some of the pre-order weapons are being released as regular DLC. http://www.siliconera.com/2012/03/05/jihl-nabaat-d