The fact that you can already play the PS4 title on PS5, have they stated anywhere what will be unique to the PS5 version? My guess is that it'll have better graphics support, similar to the PC port, but was just curious if there has been any official word?

No official word, but I assume the replay feature mentioned in the latest producer letter would be implemented (and sadly I don't think PS4 VF5US will get it). I hope the game has enough additional features added that consumers see it as worth purchasing another VF game (even though they already have VF5US). I mean, 4k graphics and roll-back net-code is nice upgrade from Ultimate to REVO, but not necessarily a big enough upgrade for non VF-fanatic consumers to make the purchase.

So reading between the lines, it appears as though the PS4 version is no longer being supported?

It feels like that is the case. I tried to get clarification from SEGA, through various means, but have not gotten a reply back. Maybe during Combo Breaker we get more info.