Also, you know, it's pretty unfair of the game to present you with a bullet point list at your bed roll, for 'who do you want to pick' and you might have four or even five options.... and yet there's no "Invite both X and Y" option anywhere... This is supposed to be a party, after all...
(Note: said at least partially in jest; I absolutely do want poly conversation options eventually, somewhere in the game, but I agree that the way it's handled right now is pretty tacky and forced in the everyone-at-once-right-now set up)
Similarly, being able to "romance" multiple companions (either sequentially or simultaneously) over the course of the game could add some interesting dynamics. One of my problems with the party is that companions get so snarky if you choose someone else, but since they've all decided to proposition me at the same time, my only other option to choosing one of them is to choose none of them.
I am assuming (hoping) that the romance is spread out further over the game, so then companions can be given more in-depth reactions to you sleeping with other companions/NPCs, and romances could be affected by your other romance choices. Some companions (Astarion and Lae'zel) probably wouldn't care, as long as you are also are sleeping with them. Shadowheart would say that you can do whatever you want, but secretly be hurt. Etc.
DAO had something like this iirc, where companions you were trying to woo would remark on your existing relationships with other companions, and eventually force a choice. Those were interesting conversations to try to navigate without everything blowing up :P