But consider the situation where crypto more or less takes over...
As in becomes the world's most used and accepted payment method? I don't see that happening. If they can't govern it, they don't want it.
Are dark web and deep web centralized? They're also running on the internet but there's no way to control them. The government can't even stop them.
Tell that to Ross Ulbricht and those who were operating Silk Road and see how far that gets you. I mean sure, you can create a dark web marketplace and the government can't simply shut it down. But let's not kid ourselves that people and services can't be stopped, blocked, and shut down when there is enough interest to do so.