I agree, P1 and 2 haven't aged as well as 3&4. They need some cleanup.
Well the two P2 games mostly need a gameplay revision (random encounters every 2 steps that can be fatal in a single turn before you have your own) but that would be small revisions.
P1 on ther other hands need a whole new gameplay, some retcons for better integration in the IP and let's be honest, a complete makeover of the character design.
At this point Atlus' best bet -if they want to go for it- would be to remake the first 5 games (p1 ->p4) on a single engine and outsourcing part of the development. But given they would need to do all 5 if they want to recoup the budget, they would need some massive support, motivation and time.