That's unnecessary. Motion blur would be calculated by the speed you are moving at, or aim your camera. We don't need new controls specifically for motion blur.
The way you talk about it, you make it seem like it'd be like the Source Engine's in game motion blur that can only be seen while moving fast, the edges of your screen blur, or when you're just flailing the screen around
While that'd be nice, i'm also hoping that, for example, if other players, vehicles or whatever were moving at a high enough velocity, they'd be motion blurred, kind of like how things are motion blurred with the Source Filmmaker or Team Fortress 2's replay editor
Yes i am using Valve's stuff as an example, but only because i don't play many other games that have good looking motion blur