The very problem of deflation he speaks to is only a problem if the deflation isn't predictable.  If a currency deflates at a few percent per year as I would expect bitcoin would if it had wide spread use, the interest rates charged would be adjusted accordingly just as they are with persistent inflation.

The deflationary spirals is largely the symptom of excessive debt creation and the deflation is caused by that debt not being paid (default) which basically reduces the money supply in a fractional reserve system.  When the federal reserve prints money to buy mortgage backed securities to prevent this deflation it does address the symptom, but it doesn't change the fact those debt instruments never properly reflected the underlying economic reality.  This causes a distortion in markets where the asset prices (morgage backed securities, US treasuring etc) appears to reflect greater future production than will actually be available.  Let alone the huge moral hazard caused by telling well colluded banks that if they make bad investments they won't have to suffer the losses.

We will see a lot more stuff like this.  But in the end real world results are what matter.  I hope if we push forward developing BitCoin and successive and related technologies in time the empirical reality will overwhelm this Keynesian non sense.  Keynesianism is better understood as an excuse for government spending and monetary manipulation for those that pay the salaries of those economists than a useful model to understand economic reality.