Well, one last thing I'm still holding out a modicum of hope for is that these companions will be at level 1 and we will have complete freedom to take them in whatever class direction we want. So, for all of them we'll lose one level (their first), but after that we could set them up any way we want. In such a scenario, I could potentially keep someone like Karlach but dump her stupid barbarian class and multiclass her into something else entirely.
According to this guy who interviewed Sven, multi-classing won't be in at Launch. I don't know if that means PC launch only or both PC and Console launches, or when it might come after that.