I don't presume to be able to predict so far into the future as required for BTC to have reached a valuation of $10 M.
But in fact, if I accept that possibilty, and you accept the possibility that governments ban the private use of BTC, even if they fail at enforcing it universally, you should see we have a problem here. Both statements can't be true, or hardly.
As a matter of fact I think they're directly correlated: if BTC eats gold's lunch (BTC = $500k), you can bet enforcement of the public monopoly will ramp up. If it hits $10 M, it will be total.