I'm dropping the question of adding more kids and focusing on the school idea now.
I don't think it would necessarily be that much more work, especially if it was parsed out over updates. We already have several repeatable threesomes (plus the potential fivesome that could be worked into Qetesh or the sixsome for Nergal), and Victoria will mention you knocking up Rosy during Gwyneth's pregnancy questline. So start off there with bringing in the Weirdwood folk (including poor Mia who would probably take it the worst), then either the elves or Qeteshans (letting everyone in your harem know what happened to Alice could make for a fun scene), and then maybe the giants (although we'd need to finish Hilde's pregnancy first so that Frida can freak out about that before getting even more mad). I'm leaving the various monster wives out of this hypothetical, and probably Nergal too (at least until the endgame) because that would go from jealousy and heartbreak to hysteria, terror and war.
You could have just a few new smaller scenes (threesomes/foursomes) and maybe have a gathering that you can plan for in advance (PTA orgy?). It wouldn't be done in one update, but in theory it shouldn't be any harder than the coding to set up the current threesomes (both girls available and horny) for those smaller events.
While I like that idea the coding is still gonna be pretty big. You need to have a version of these threesomes/fourseomes/fivesomes that have different girls in them (excluding monster girls that's 17 girls currently, I'm including the Succubus cos she can hypnosis others). Then you have to have versions of all those scenes that include all those girls pregnant as well. Even implemented over time it all feels very arduous & incredibly data heavy.
Then we have all the women that Tinkerer is planning to add as well. I feel if this was implemented earlier it would all work & be really good but currently its gonna take time. Not saying it cant happen just that it would definetly have to take the backseat to Main Plot & the last 3 girls who need preg content (Vix, Hilde & Beth). Perhaps one day this will be worked in I just cant see it now. It's so much to weave in at this point in the game & I cannot see most of these girls ever being ok to find out MC is (essentially) cheating on them.
The Qeteshians, Nergalites, Goblins, Vampires, Victoria, Gwynneth & Jenny are all very open & are not deluded with believing that MC is "loyal". But the Nergalites, Goblins & Vampires are (currently) at odds with Qeteshians & probably wouldnt wanna be in a orgy with them (& vice versa).
Liandra & Luthien may share MC bit I dont think she would be happy to see him with anyone else as well. Her reaction to her mum was pretty bad. Frida may be able to come around with Hilde but again I feel beyond that would cross a line.
Beth, Mia, Rosy & Maghda I cant see being happy at all with this revelation either.
I like the idea of a big orgy in the Temple, but again that needs preg versions as well. So I'm not gonna hold my breath no matter how much I would love it.