We have a few of those unverified-but-probably-true early flying get bits from this week's Weekly Famitsu concerning Final Fantasy XIII-2's download content, and even a tiny mention for Final Fantasy X HD.
Square Enix previously said that Lightning would appear in the game as DLC. Famitsu reveals that Lightning will appear as a coliseum character. Defeat her, and you'll be able to make her into a party member.
Lightning's DLC goes beyond just the character data. Square Enix also plans on releasing secret story episodes for the character.
Outside of Lightning, FF fans can look forward to classic Final Fantasy series bosses for the coliseum battle mode.
These revelations come from what appears to be a general interview with reps from Square Enix's 1st Production Department (I'm not sure who the reps are, but XIII-2 interviews are usually with Motomu Toriyama and Yoshinori Kitase). The interview also reveals that Square Enix is hoping to expand the XIII-2 story outside of just DLC, with novels and so-forth. They hope to include Sazh and his son and the Chocolina character in DLC or novels. Noting that the Japanese market is changing greatly, they say that they'd like to consider a variety of things for future developments.
There's one bit about Final Fantasy X HD in the interview. The staff says that it will be a bit longer before we get screenshots. However, they hope to not take too long in releasing the game.