They're already unenforcable -- against criminals, who steal them (both wholesale and retail, sometimes even from police evidence rooms) and illegally import them.
I have to admit that I am always surprised by people who confuse and conflate the notion that something is possible with the notion that laws against that possible-to-do thing are thereby rendered unenforceable.
It is extraordinarily easy to acquire an automobile with a top speed exceeding 75 miles per hour. They can be found readily on our city streets, in the garages of our homes, all across America. Millions of such vehicles exchange hands, legally, every year. Shockingly, that doesn't actually render laws against speeding unenforceable--even though every driver has access to technology with which they can speed, available at the twitch of a foot.