Persona 3 and 4 don't need full-blown FF7R-style remakes. P1, for what it is, is also not really in need of a remake either. So regarding whether we'll see a P3 remake or P6 first, I believe (or at least hope) the answer is P6, unless we're talking about relatively modest enhanced ports/remasters of P3/P4.
P2 is the only entry that could greatly benefit from a remake IMO... it had by far the worst gameplay of the series (yes even considering P1's godawful grid-based combat), so seeing that get fixed would be nice. And the story/characters/concepts are interesting enough to deserve getting fleshed out in a remake.