With how many routes I've tried I'm suspecting mpreg is really underdone so far.
In public version. Mpreg is something that comes at the very end of a route (the good ending for the main cast) within the epilogue that will happen after day 4, and is hinted in those who dun you up teh butt smex scenes. As in what they say and do changes up somewhat, some more than others, during the scene with the fact they know the player can or at least know something's up.
The patreon version have epilogues (purely bonus content as a thanks for the support) after every gameover that changes based on what major they're in. Just like how of the gameovers changes based on what major you're in.