The regression theorem argument as applied to Bitcoin is the worst kind of anti-empirical apriorism that Austrians are criticized for.
Let's suppose, for the sake of argument, that Bitcoin were circulating as money, in every sense.
It would be pathetic and ignorant for an Austrian to say, "Nuh uh. It can't really be money because Mises says it couldn't have become a money."
If Bitcoin ever does become as liquid as the dollar, then we will have to say one of two things about the regression theorem:
- The regression theorem is wrong. Mises implied Bitcoin couldn't be money, yet it is money, so Mises is wrong, or
- We are misunderstanding the regression theorem. Somehow, Bitcoin satisfies the regression theorem, but we don't understand how or why, so we have to reinterpret what the regression theorem says.
One way or another, if Bitcoin ever becomes a money, then it will be a money. That will be an empirical fact (by the assumption of my thought experiment). It is the worst kind of Austrian apriorism to deny empirical facts because they contradict your theory. If empirical facts contradict your theory, then either your theory is wrong, you have misinterpreted/misapplied your theory, or the empirical facts aren't really what you think they are.
What good Austrians typically do is say that the empirical facts aren't what you think they are. For example, if you observe that quantity demanded of a good increased as the price increased, you typically respond that it must have been an increase in demand. It's not that demand slopes up, but rather, a downward-sloping demand curve shifted to the right.
We're not denying empirical facts to fit our theory. Rather, we are using theory to interpret empirical facts, because the data do not speak for themselves. Any econometrician will say that a statistical analysis is only as valid as the model specification.