i think the american government is more likely to indirectly target mixers by implementing "know your customer's customer" standards like those seen in the FATF travel rule. basically, they'll pressure services to blacklist non-complying services like mixers. anyone who doesn't fall in line is at risk of adverse government action. the exchanges police themselves.
Right, they going to like "flex" their muscle again, maybe ala BTC-E seizure most likely in the future. Interpol/EUROPOL also have this sort of mentality as in the case of Bestmixer.io last May.
I suggest everyone to brace yourself next year about this new regulations and policies. Maybe some exchanges will stay in their ground and try to protect themselves, but which pressures coming at all angle, just a matter of time before they succumb. And it will create a lot of mess, maybe exchanges will run to a supposedly safe haven countries, who knows.