After support Nintendo for so long, since the WiiU actually with ZombiU, Rayman Legends, Rabbids games now with Mario+Rabbids and many other great games for their systems, I think it's nothing less than fair that Nintendo supports Rayman, an iconic Ubisoft character, as one of the new fighters.
I think it's also safe to say that one of the newcomers will be a Pokemon of the new game, but I think it will be one of the leasts inclusions, if not the last.
The others, I have no idea, but I'm fine with the idea of adding more recent characters or characters from games that are coming, to keep the game updated with recent games too.