Now that we have confirmed non-origin companions:

* I am going to guess there will be eight origin companions. Obviously Karlach is all but confirmed, but I think Larian surprises us with two more.
* I think we will get multiple non-origin companions that are both part of good and evil factions.
* I am hoping that they spread the non-origin companions through all of the acts so you can keep meeting people and potentially changing your party throughout the game.