I think you might be overstating. The US dollar is not backed by an asset because it is an asset. At this point, the dollar is backed by the government, the government's authority, its military power, and the future value of its debt. That is not gold, but it is not nothing either.
Tether intrinsically has none of these, but because of its adoption by many exchanges, it's convertible into other currencies that have more intrinsic value. So as long as it remains convertible, it will continue to have value.
Also the gov creates more supply to the dollar than the tax demand always, so its not really clear. And most taxation is a percentage of income or value measured in dollars itself.
This argument never clicked for me: where is it coming from?
The intrinsic value of USD is consoling, because it prevents the value of USD dropping to 0, hence there will always be a possibility of the emergent value reappearing.
It's also worth pointing out that income doesn't always translate to inflows of physical dollars. Complex corporate accounting standards often result in recognizing revenue before any cash is received, and non-cash transactions that affect income.
What sets that exchange rate is demand for bitcoins, and demand for bitcoins would be equivalent to what you can buy only with bitcoins. So, I guess in a way that tracks to exactly what you describe. The part that doesn't track is the profit potential. Currency speculation is an interesting thing, but it doesn't usually track with the use of a currency.
I am pretty bearish on the long term viability for cryptocurrency growth, though. I expect transact in bitcoins about as often as I transact in any other currency...almost never. There are no wages, products, services, or geographic areas that require the use of bitcoin.
This is what has happened with the U.S. and China over the last 3 decades. As Chinese goods became more competitive on the global market, American export dollars started to flow into China. China refused to remove the USD/RMB peg, which created a long-term current account deficit in the US and made American goods & labor non-competitive with China. When they finally did remove the peg (after significant political pressure from the US), the value of the RMB rose significantly: it was 1:8 a decade ago, it's now 1:6.73.
Over the short term there are a lot of conflating factors - pegs, speculation, interest rates, wars, creditworthiness, etc. But over the long term, the "backing" for any currency is what you can buy with it.