Natural guesses for next version are, imho, either more Grandma, extra threesome scenes (Kira-Mom & Kira-Sam being two i kind of expected to have already come up) or both. Less obvious combinations might be Mom finding out about the Sam-Julia threesomes and that leading into a foursome, Janet finding out about Edna or vice-versa and that leading into Aunt-Grandma super secret threesomes.
For something off the curve, maybe Sam joining into one of the video sessions on Vicky's place (videogame-related costumes & Julia also joining into roleplay optional), Kacey upgrading from restroom shenanigans into fullblown exibithionist hijinks in the park at night or maybe some post-vacation scenarios (though that last one i don't expect to come up very soon at all, still so much that can be done with this summer).
