I think this is a kind of picky request. I have never encountered a situation in which, after changing my position, I could never use my 3 missiles on a target. And trust me, in my solo wizard playthrough, I was using multiple magic missiles in every single fight.
The paths for the missiles are already in place. If it's more resource intensive to implement than it seems, then I agree that there are more important changes to worry about. It just doesn't seem like it would require that much time and effort to allow you to pick which one of the three paths you want your missiles to take.
I don't even care about the spell that much, the idea just seemed like a good an easy fix.
