In the Panel From Hell interview, toward the end iirc, Swen stated that there would be more companions, races, classes, and features introduced throughout Early Access.
5e is also really flexible in that you aren't limited to absolutely needing a certain class (or in this case, bringing along a certain companion) so even as someone who prefers to hoard companions throughout the game and would even prefer a bigger party option, I don't think locking companions after Act 1 will have us feeling boxed in with few options or risk losing xp/loot.
