Definitely could see Monero getting banned. This would happen if any U.S.-based exchange were forbidden to trade this currency.
Mining is already taxed. It falls under existing mining laws where anything mined is immediately taxable. Small-scale mining will still fly under the radar but slowly large-scale mining will be tracked via checking electricity use.
I don't think mining machines will ever be directly taxed with a "stamp tax." That'd be very British and very un-American.
The thing with banning a privacy coin like Monero is it is the hardest one to ban. You basically have to admit to them that you use it because they have no way of knowing otherwise. They can ban businesses from accepting it, and ban banks from converting it to fiat, but everyone is just going to use BTC for those things anyway.