I agree with you, i think that the first 3 you said are pratically confirmed in future updates, but i think that the others are maybe too optimistic? Sage x Quinn it's ok, maybe a foursome with riona or camila, but a threesome with Josy and Jill i think it's impossible, Jill is too pure and if she does a threesome it will be only with Bella, with another character i think that the character of Jill isn't done for this and i like this game for this reason. Every character has his unique nature and every character is different, it can't be possible not find someone who you don't like.
For Maya and quinn is a different speech, i really HOPE that this will happen, but i think that if this happen, it will happen between Maya and Quinn only, not a threesome but a lesb scene, maybe if she and josy will break up and in a dark moment maya will do this bullshit with some regrets after this.
a threesome quith Elena and John boy can be done but i don't think dr pinkcake will create a scene like this because i don't think that all players will like that.
I want to add a new prediction that i think it will happen if the relation between quinn and tommy is going to go like this:
Quinn x Josy (And maybe Maya): For a simple reason, if Quinn wants to make tommy angry the best choice is to fuck his step sister. And if in that moment Josy is still in a relationship with Maya, to convince Josy she have to convince Maya too. If not she will only fuck Josy. (I would like to see something like this, because for the MC probably this would be another drama like when he found out that Maya and Josy were together, i loved that part and if the MC would feel betrayed by Josy and also Maya to "Cheat" on the relationship between the three of them)
PS: My favourite character is Jill, yours?