I was always fairly sure that P5 would end up on Swith, but not because of Joker in Smash. While I think it increased the chance, I didn't think his inclusion meant it has to happen. A lot of different companies want to collaborate with Persona 5. Fashion brands, popular Japanese mobile games like Granblue Fantasy and Puzzle & Dragon, and studios like Omega Force and (probably) Arcsys.
But I did not think it would be called Persona 5 Switch. Maybe 'S' if there were some substantial differences, but not Switch. If it's the same game as its PS4 counterpart then that would only cause unnecessary problems and confusion that can be easily avoided.
Thank you, this post pretty much sums up my thoughts. I still want P5 on Switch, but it seems unlikely, after yesterday (P5 Royal infos). I didn't expected P5S to be an extended P5, after Royal turned out to be it. But still nice to get another branded Warriors, might pick it up.