On the other hand, you can't stay in HS1 forever.
Who says? This game looks fucking great as is, and changing it to make it look very slightly better seems like it'd be a huge waste of time. Especially since as
Walter Victor points out, for continuity sake Jestur would have to re-render the entire game. Changing to HS2 without doing that you'd be left with a very jarring style change once you hit that point in a playthrough, which is never a good thing.
Is there some AVN rulebook somewhere I didn't know about that says you can't keep using the engine you've already successfully been using for years to make a great looking game once X number of years pass?
But still using HS1 in 2030 and beyond is a scary thought.
Even if this game is still being made and not completed yet 5+ years from now, unless Jestur starts letting the quality slip, it'll still look great then. Why is that a scary thought?