It seems more likely and suited to be things like weapons and costumes, and maybe additional Materias (though both they, and weapons could easily just be added in the game.)

I still don't see the point of DLC, unless it adds in something the developers forgot about, didn't come up with until later, had no time to include, or had no idea how to include in the game. I'm sure it's a way for them to get more money, but I like it better when things are either found/earned in game, or by programmed cheats (like a fighting game where the only way to get a character legitimately is to enter a certain command at a specific time.)