I could see all the people flipping houses jumping on this strategy, too.  The real question is whether the size of the loans becomes large enough to become a problem.  I don't think it will because the Fed can reduce lending by raising interest rates or shrinking M1.  The housing bubble was bad, but the Fed stepped it before it became a serious problem for the dollar.

The real speculative attack, if it comes, will be from a foreign central bank or government.  It could be a purposeful attack on the dollar or just some dictator's get rich quick scheme.  The foreign entity would print *their own* currency to buy bitcoin.  This would tanks their currency, but they don't care because it will push bitcoin up in dollar terms (by reducing supply.)  Eurodollar (non-fed regulated) banks could also potentially pull this off.