If we look strictly at present mechanisms (ignoring the fact that the definition of the dollar could be changed as it has several times in the past), the dollar is much closer to a Ponzi scheme than Bitcoin is.

I think you've made a distinction without a difference. Bitcoin assets, and income that is denominated in Bitcoin, is every bit as taxable under US law.

It's true that attempting to conduct your entire financial life in Bitcoin won't save you from receiving tax bills that are denominated in dollars. I think your more immediate problem, though, would be that it's probably impossible for someone living in the US to participate in Bitcoin without owing someone a bill that they will expect to be paid in USD. It's difficult to transact Bitcoin without Internet access, for example. And that'll get you long before the IRS sends police to knock on your door.