Strong possibility because of upcoming events and the fact that they don't have a sex scene yet:
-Luna
-Penny
Less likely but are due a scene (either one could work):
-Nancy (Pending Beach date and continuation of Rome server tryst)
-Nova (Last scene was 0.3, could possibly happen post-costume party)
If both nova and penny get a scene, I think it would be more likely for nova to get hers at the party and penny after the party.
My reason is that in pennies memory that we saw, she fantasized about going to prom, getting escorted back and then getting a kiss.
Which I think would make for a nice scene if Orion does that for her after the dance party.
In particular in regards to penny it's already a theme that she likes it when Orion shows that he has listened to her which would fit in with that.
It's just as likely that a scene like that happens without any prior scene with nova.