Well, if you had a rotating cuff internaly could line the bullets with the firing chamber, similar to the P90s, it would just have to be set so the rotation speed is high enough to make it an SMG RoF. Its a possibility, but I think in reality it would work. Good nice design.
Shift a few things around a bit, and you have a decent weapon. I would (after the tweaks of course) make the magazine (keep this orientation) and load perpendicular to it's current insertion direction or from the side or top.