My guess is that there will be two categories of companions. Origin Characters (Companions) and Companion Characters. I'm assuming that we have probably seen all or at least most of the Origin Characters. These characters have more lines of dialogue than anyone else almost definitely, and require the most work toward developing in general. I'm assuming that later in the game, possibly after the end of Chapter 1, we will be introduced to more potential companions who are also heavily developed, albeit to a lesser degree than the Origin Characters (who, to remind you, are also player characters).
Companion Characters who are not Origin Characters would have less potential for being driving forces behind the storyline, while having their own plots going on. They'd have voice acting and other major development, but little enough to manage to pump out additional characters.
I'm probably wrong about all of this, but I came around to this theory just by thinking about Minsc. I don't envision Minsc being a selectable character at creation. I could see him being excluded from the game entirely, but because he is the most popular character in the series bar-none, and in 5th edition is alive per the canon, it makes more sense to me to include him than to exclude him. Potentially there may only be a cameo; there may be a referential cameo, but total exclusion? Not so sure. I suspect he will be someone you can recruit down the road, but who can never be a main origin character.
