I think it will be Luna, Nova and Penny for sure. We have the festival thing with Luna and the costume party with Nova + Penny.
I think the most likely candidate for the 4th scene is Nancy because Annie, Dalia and Alex all had scenes in 0.4 + we have committed to doing stuff with Nancy already.
Unless of course the dev decides to do a Calypso sex scene which I would personally like even more than scenes with the 7 girls because she is tied to the story in a way that they are not. However I doubt this will happen - we need more character development with her before it does.
As a side note I hope we get a card for Calypso as well in the relationship screen as she is important to the story, she will likely have scenes and she like the other girls will have different outfits etc.