I don't think the movement system is going to change to allow multiple characters to be selected. The way it is now, it is extremely "controller friendly" and since controller support is going to be added, I doubt they are going to create an entirely new movement system that will be completely separate from the controller based one and only work with mouse and keyboard. The movement system is also very "multiplayer friendly."
I don't see how changing it for mouse and keyboard would prevent Larian from sticking to the same questionable scheme when playing with a controller.
But still, let's not waste our time worrying about what we think they are going or not going to do. This is not about making predictions, but judging what's there.
Let's stick to the facts; does it suck or it does not? It does, it fucking does. It sucks so badly it's almost universally loathed by anyone who doesn't work at Larian (and maybe even among them) or isn't "Mr Not so fast".
In a forum where even arguments about crap being edible have their defenders, that alone should be an alarming tell that something is wrong.
I don't think it sucks as much as you think. There's definitely problems, but I think they can be solved by making tweaks to what's there as opposed to completely changing it to be more like the RTS style of BG, Pillars or Eternity, etc.
If you get rid of the headaches of things like stealth, pathing, etc. Then I really don't think it's that bad. I mean this system was basically used in DOS 1 and 2 and tons of people love those games.