What will happen if, in a moment of weakness, the user thinks to just "W" into the middle of the street? They weren't actually going to, but with a BCI-controlled wheelchair I feel like it's hard to make this distinction.
But it doesn't happen (at least it hadn't happen to me, obviously). You cross streets by moving your legs thinking of "W" or maybe about jumping, moon-walking, climbing or flying or anything and it doesn't make your legs jump or to mimic Jackson.
I'd bet that practice will make brain controlled things like this, you will be able to control them while thinking about anything, including alternative approaches to control these things in the current situation.