There will be more companions/origins, Karlach being one of them, thanks to datamining, and her having a tadpole. Other mentioned can't be companions, as they can't be origins - unless Larian will add non-origin companions on top of 9ish? (not sure on the number) origins. As far as I am aware there is absolutely nothing suggesting that Halsin and Co. might become anything more then "camp followers" outside wishful thinking of some.
Having more companions per chapter or something like that would be nice, assuming the game would be designed for it, but:
1) if larian would be willing to support party of 4 or 5 or 6 then why wouldn't they do so from the get go?
2) It would be odd for Larian to support varied multiplayer experience for different chapters.
3) If my hunch and my reading of old Larian statements are correct, then the problem OP describes won't exist past chapter one, as BG3 might follow D:OS2 formula and ax spare companions at the end of chapter 1, leaving us with 4.
