According to a recent interview, it appears that the roster for Square Enix, Koei Tecmo, and Team Ninja's Dissidia Final Fantasy NT will continue to expand.
Dissidia FF NT Archives
With Type-o on the Dissidia slate now, it's more likely than ever that we'll see the fighter branch out.
While the handheld Dissidia games were more of an RPG with a compelling story mode, you shouldn't come to Dissidia FF NT for the the story It isn't anywhere near as cringe-worthy as the story mode of Marvel vs[...]
And maybe venture a guess or two of your own.
We played Dissidia FF NT back during the game's closed beta and found it to be both bizarre and perfect:
"It isn't Smash Bros, and it isn't Tekken. Dissidia is honestly more like, well, an RTS than a fighter Which is why it makes perfect sense that Koei Tecmo are partially responsible[...]
The developers of Dissidia Final Fantasy NT had a bit of fun teasing the six additional characters that will be coming to the game as DLC add-ons.