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.