A PS2onPS4 case could happen, but I don't think it'd be happening soon at the moment. Persona 3 Portable/FES combination and 4 Golden remaster on PS4 is pretty much a pipe dream though.
And yeah. While there might be small things still coming and going from here on out, Persona 5 will be used for mainstream products. So Persona 5 arena instead of Persona 4 arena. Persona 5 Dancing instead of Persona 3/4 Dancing (If they do one again). Morgana instead of Teddie on Twitter. MAYBE something like Persona Q would be done again. It seems like Persona 5's using 20xx for it's date though which would make things interesting from a crossover perspective though.
And yeah. While there might be small things still coming and going from here on out, Persona 5 will be used for mainstream products. So Persona 5 arena instead of Persona 4 arena. Persona 5 Dancing instead of Persona 3/4 Dancing (If they do one again). Morgana instead of Teddie on Twitter. MAYBE something like Persona Q would be done again. It seems like Persona 5's using 20xx for it's date though which would make things interesting from a crossover perspective though.