You know. The Persona series has nothing to do with Nintendo at all. So I guess this means characters from non-Nintendo games that don’t make sense can be in smash.
The Persona series doesn't exactly have
nothing to do with Nintendo. It is an offshoot of the SMT series which is majorly prominent on Nintendo systems. The newest one is coming to the Switch, for example. Plus, there are Persona spinoffs that appear on Nintendo systems. Persona Q2 features Joker and is a 3DS game.
With that said, I still think you're hitting toward a valid point here. While Joker appears in Q2 and the SMT series is large on Nintendo systems... Persona itself really isn't with all of the mainline titles being Sony exclusive (someone correct me if I'm wrong). And the trailer is clearly pointing toward Persona 5, even saying Super Smash Bros Ultimate X Persona 5.
No matter what anyone tries to say, this is awkward. Persona 5 is exclusive to PS3/PS4.
I say this being a big fan of Persona 5 and actually being
personally excited for this character. It just doesn't sit right either way.
(I know, the Fire Emblem characters, Sonic, Pac Man, and Bayonetta have nothing to do with Nintendo, but it makes sense. A Persona character in smash doesn’t.)
FE being a Nintendo series has already been addressed, so I'm going to move onto the giant elephant in the room that you failed to mention: Cloud. When Cloud was added in SSB4 his only appearance on Nintendo systems was a card cameo in Kingdom Hearts Chain of Memories on the GBA and the Theatrhythm games. There has never been a more "has nothing to do with Nintendo" addition than Cloud. Cloud is practically the mascot of the Final Fantasy series once it left Nintendo systems.
A port of Final Fantasy VII is now confirmed to be coming to a Nintendo platform, but... Despite being a general video game icon, Cloud's addition was very strange.
You know what that means. I don’t want him, but Sora has a chance.
Hey, better than Cloud. At least Sora has several titles on Nintendo systems to his name (Chain of Memories, RE:Coded, Dream Drop Distance). However, apparently Sora is Disney owned and that makes things more complicated for him.
Personally, if we're just going to throw the rest of the roster to 3rd party characters, Sora is actually one I'd personally really want. Phoenix Wright from Ace Attorney and Amaterasu from Okami, as well. Sadly, I don't think any of them are even "likely" aside from maybe Phoenix Wright. I don't even know about that.
Instead we'll probably get a lineup of 3rd party characters that have nothing to do with Nintendo. *sigh*