Yeah, I am thinking P3/4 characters arep pretty likely(Heck, matbe even P1/2, as there was a refrence to it). I am curious if this game takes place after base game P5 or Royal though.
I've kind of replied to this in the Joker thread, but why not mention things here!
I've been up and down on P3/4 characters, as I'm starting to think that this game may already be one of the biggest Warriors IP crossovers without them, especially as Joker has his Wild Card abilities.... I have seen the Tweet about the colours and while it is obviously a reference, the Tweet putting them in the order of P1-5 makes it feel more meaningful to me? I don't think it was a tease, just a reference. Also, canonically, the P1/2 cast must be in their 40s by now, I think...
ATLUS has split their timelines before, but I don't think they would ever risk making a spin-off game
non-canon. These are the people who made three dancing games canon, one of which even features you saving the world from a destructive God with the power of dance. They don't cut canon corners.