Honestly I think this game has kind of hit the end. I mean, the game was about:
- The MC fucking everyone around him, including his daughters => Done
- knocking up at least one of them => Done
- Sandra slowly getting to grips with everything that the MC is doing => Almost done
I hope that Nef can find the energy to wrap up the open ends and give this game the ending it deserves.
Basically it only needs one huge harem scene with Sandra and all other girls, a few scenes leading up to that, and a few scenes with a kind of epilogue.
Then Nef can focus on developing another game with different characters and storylines but hopefully a similar mood.
Personally I wouldn't even bother with retroactively implementing non-harem options which nobody is going to play anyway.
There is definitely stuff that can still be added to the game, and, being a slice-of-life kind of story, it could go on for ever. But in my opinion, it will not make the game better.