When you think about it there is (not?) much they can do to change the revolver or semi auto pistol either.
I don't know about that. I'm fascinated with ideas for making a semi-auto legally simulate full-auto. For example, I am interested in the crank devices that can be mounted on Browning 1919's. There are other crank devices that simulate full auto fire. I liked the Akins Accelerator - no I didn't buy one, but even though BATFE says it's not legal, I think it is - problem is no one has challenged this in court, and probably won't. But, that's a matter of legal opinion.
So, I came up with this idea: A crank-style device, but in the form of a geared pump / piston. The geared pump would mount under a semi-auto rifle. with a piston that presses the trigger as you pull the pump - maybe 5-6 runds fired per push or pull of the pump. Would BATFE approve it? Who knows - isn't any different than a crank device. The bigger question is could I draw it or make it? No, I just don't have those skills.