Personally, I think there's never gonna be a "AAA" porn game. The production quality will definitely improve but I can't imagine living in a world where a porn game has the same quality as RDR2 sadly.
Tbh not really, but I played one recently called sakura gozen and it completely caught me off guard. No spoilers but if you want a game with a surprisingly engaging story, check that one out.
You can have a 10 min prologue but after that, you gotta start pumping the gas on scenes. The only exception to this is if you're playing a corruption game, but even then you should have some minor scenes sprinkled in.