[loveistheanswer]

>The main avenue would be by getting rid of the sanctioned on/off ramps for crypto (that is, crypto exchanges), leaving only the illegal on/off ramps which I'm sure exist.

From what I've read it seems its only the stupidest of criminals who are using exchanges like Coinbase to cash out, because that's the easiest way to get caught.

[nneonneo]

What you want to attack is the on-ramps, not the off-ramps. Make it really hard to legally acquire cryptocurrency, to the point where a company would probably have to break a law or two just to get their payment together. That, plus criminalizing ransom payments, would go a very long way to stemming this tide.