With the viability of new technologies, I see a time in my life where a Sci-Fi weapon will be commercially viable. Railgun, Gauss cannon, laser gun, something along these lines.
Maybe in your life time - but - not in mine...
Then again, I'm only 61 and break throughs happen all the time so who knows for sure?
Anyhow to answer your question with a serious answer,,,
All the BATFE has to do is classify any future weapon as a destructive device & they've got it covered.
Might as well face the sad fact that our right to keep and bear arms has been changed to..
The right to keep and bear arms made prior to 1987.