Pretty sure it can run on the Vita with some graphical compromisses, as it's a PS3 game on its core.
And if its going to take a while like the other portable versions, a new PS handheld could easily hand it as an enhanced version compared to the PS3 version, and closer to the PS4, so they would likely pick it as well, the question is, will Sony even make another handheld? If the answer is no and there is no deal between Sony and Atlus for exclusivity, it can surely land on the Switch.
Oh I'm sure they could get it to run on Vita. But if they follow their pattern for portable Persona ports, then P5 Portable may not come out for a few more years. At that point I'm not sure they would be interested in supporting the Vita. And so far it doesn't sound like Sony will make another portable. Asuming they don't, Switch may be the more attractive option.
Yeah, that's what I said, if it takes a while it would have to land on a new PS handheld if there is one, otherwise if there is no deal between Sony and Atlus/Sega and this handheld doesn't come, it could land on the Switch, indeed.
I think it's more likely we get a goty/complete edition for the PS4 itself in the near future, just like FES.