It's not that the dollar couldn't be unseated, it's just that there isn't currently another fiat currency in the world that could take its place...or even a reasonable combination. I could see Bitcoin taking its place faster than the other options I've heard.

The dollar is up slightly over the Yuan from a year ago, up sharply vs. the Ruble, and up slightly vs. the Rupee. Demand for the dollar does not seemed to have lessened noticeably, at least over the last year.