Happy to hear you liked the game so far.
I could in theory implement the pregnancies already, by doing a time-jump in the story or inventing some plot device as you mentioned. The trouble is that I'd need to deal with the development of all those pregnancies and also provide content for the path where the girls aren't pregnant.
As the game isn't rendered in real-time, any branch adds a lot of extra work. Also, when the children are actually born in the middle of the story it would create another problem where I'd need to deal with the MC and love interest being parents, raising their kid and so on. Not sure if changing diapers makes for a titillating experience...
The pregnancies are optional, instead of the True/False checkbox at the start of the game, the choice will be offered through dialogue, like I did in my other game, Sisterly Lust.
The virtual sisters storyline will continue in a future episode, if you didn't choose to wipe the simulation. I do try to follow up on any of the dangling plot threads I've created, but it sometimes takes a while to get there.