We just reached month 6 of the development cycle, the update should come out in 5-7 months. Every friday a report is posted here with some informartion from the developer.
The future threesomes with Sage are a fun topic to discuss, while I can't say for sure who she will invite we can say who she won't with a decent amount of certainty.
Firstly it will probably be a HOT since we don't see Sage interacting with dormies.
Aerith is out due to Crabs/being pregnant, Sarah/Mel most likely out because Sage is still a bit weird with them since she thought they were cheating with Chad, Heather is very unlikely due to Tommy even if they are likely to break up in EP11. Ashely is also out due to her ties to Anthony & Derek.
That leaves Camilla, Riona, Elena, Lily, Josy & Maya and Quinn.
M & J are very unlikely to be invited since Sage is aware of them being a couple, plus the shaky status of the relationship in the non-M/J path. Maybe after they break up, but that would still take a while, so I only see either of them as a possibility in Season 4.
Camilla is one of the best bets, she even had plently of focus in the last EP in the pool game.
Riona is also very likely to be invited, but its not going to happen in EP11 for obvious reasons, even though I'm sure she will be freed shortly after being taken.
Elena could happen, even though we can only get progress with her in the other path as of now.
Lily is the other most likely choice, no drama here.
Quinn also could be invited, but I find it more unlilkely for now since she already had a threesome with Sage back in EP 8.