You know there's nothing wrong with making one ending the Canon ending. I've seen plenty of authors/devs that wanted to make one ending the canon ending and at the end were pressured by the loud masses not to make a canon ending. I just wanted to say this is your Story/Game you choose the ending. Even if it is the Full on Harem with pregnancies or Martha Solo route with pregnancy it's your Choice.
But if I can say my Opinion here it would be the Full on Harem with Pregnancies that I would make the Canon Ending in the Spin-off or even a Sequel if you change your mind until then maybe
My main playthrough is Full Harem, Incest, Full Pregnancy, but it's not the canon playthrough. Every player will choose his canon ending.
I want the next game to be more focused on a smaller cast (I learned that having 28 LIs is too many), so it will be around 8-12.
Doing a direct sequel will mean keeping the 28 LIs from My Dorm (Emma would be 36 when
her first daughter is 18, but Meemaw would be 84, and Norah 63) and adding the daughters. Daughters the MC has known since they were born (he will be a present father) but not the players. And there will be ~40 daughters over 18 after the epilogue (in my main playthrough)!
The stories with all of them will advance at a snail's pace, not seeing some of the LIs for many updates.
And you have to add the new students who would arrive between the endgame and the epilogue... A game like that would be unfeasible for a one-man team.
Even if I grow enough to hire employees to help, I will always do the writing (to me, the most important part among a lot of important parts) and give the employees the translation job. That will save "only" 2-4 days per update, so not too much bigger updates.