I'd assume there has been half a dozen threads about this already, but one might have to dig a bit.

If we forget about all the things that Larian has publicly said (if somebody has the complete records of this somewhere, I'm in, I mostly know about the community updates), and all the things that people have been speculating, with upper bounds because how much work Larian wants to put in each companion ... meaning if we forget about companions having to be Origins (tadpole-infected, playable as PC), then ...

- A bard. Say, Alfira.
- A druid. Say, Halsin.
- A tiefling of Rolan, Lia and Cal's group
- A boasting punk. Say, Sazza.
- An evil character that maybe we could turn away from the masters she serves. Say, Minthara. (She'd still be quite evil though.)

I might be slightly focused on the characters we have met already. But Larian still have 3 Origins companions still to release. So they can be hoped to be everything else : a Paladin, a Ranger, Dwarf, Gnome, ...