"Many private Bitcoiners will not want regulated Bitcoin, but they will be a minority." I'm not sure how many Bitcoiners you associate with, but those hostile to a move like this will be upwards of 90%. Likewise many many miners would be hostile. And I think it's a fantasy to think you'll get global hashrate to comply. If you would like to understand the Bitcoin community better (don't mean to offend), come to Miami in April and ask people how they fell about such a move.

As to starting a fork, that indeed would happen. Then it would be a darwinian battle between the chains, and the original chain (out of perview of the govt) would certainly be preferred over time. You really have to understand how utterly worthless US government regulated BTC would be. What you're describing sounds less like regulation than prohibition (of the real BTC), and governments track record of prohibition is awful. They will fail at this attempt, but only after driving the industry offshore and outside of their purview. You have to ask yourself whether the US, already at risk of losing world reserve currency status, is going to want to drive their advantaged position in Bitcoin offshore, so they're holding even fewer cards. That is what this form of prohibition would do. You may think that they believe that trying to destroy bitcoin would make the dollar stronger, but in reality, attempting to do this would only make the black market for BTC more sophisticated, driven off shore, while the US dollar loses value like sand through fingers. Will the US govt be stronger then?