This is a fascinating discussion. Big thanks to everyone contributing. I do wonder, however, if someone involved with central banking might not find it a nice play book. At least we're also discussing potential solutions.
As an American, I think government restrictions will be the hardest thing to get around. You can mention Tor and darknet and such things, but the average person doesn't have a clue about them, and probably never will. If Bitcoin is pushed to the dark, it won't ever be adopted widely enough to be a real solution. That, of course, assumes those who operate "in the dark" are a small minority. If they end up becoming the majority, we might have another revolution. That, I think, is unlikely (at this point).
As an American, I think government restrictions will be the hardest thing to get around. You can mention Tor and darknet and such things, but the average person doesn't have a clue about them, and probably never will. If Bitcoin is pushed to the dark, it won't ever be adopted widely enough to be a real solution. That, of course, assumes those who operate "in the dark" are a small minority. If they end up becoming the majority, we might have another revolution. That, I think, is unlikely (at this point).
I'm bright, but nobody ever called me a genius - You've got to imagine if I can think this through on a whim it's not that difficult for people whose business is based on staying in control.
You've correctly identified the ONLY point where the US government, or any government really, has control of Bitcoin transactions - When people exchange their bitcoins for dollars. Because it isn't tied to the USD, they can make the case that it's speculative profit and thus requires capital gains to be paid on it. There are actually several ways they could go about this, but that's the most straightforward in my opinion. As the central bank I'd want regulations to be onerous, but not so difficult to navigate that it's easier to just break the law and avoid them. Ultimately you want as much going through the legal system as possible, because you can tax that which adds to the cost of using it for the average law abiding citizen and makes dollars look better.
Once it's obvious an entity controls most of the market and is inducing these fluctuations, non-compromised mining interest groups would increase their own operations to counterbalance. This is possible because while there is no end to the money that can be thrown by a central bank, there are real technical limitations when it comes to the production and sale of ASICs, all the manufacturers are incredibly back-ordered. 