The biggest problem with the whole "deflationary" argument - And indeed, with any inflationary economy? We have a finite amount of resources on-planet. And while I certainly have high hopes of our species eventually making it off-planet (for real, not this "Billions to get a few guys to the moon for a few days" crap) - it sure as hell won't happen in my lifetime, and I see no reason to pretend otherwise.
So whenever we talk about why such-and-such a system (gold, Bitcoin, even fiat currencies such as the USD currently wavering on the edge of "negative inflation") "can't" succeed because deflation encourages hoarding, keep in mind what you really talk about - Money exists to make it easier to buy "stuff". If more money exists than stuff to buy with it, the stuff becomes more expensive. Inflation of a currency essentially just measures the inverse of the corresponding deflation of reality.
Guess what? Reality always wins. As soon as you have 100 people desperately in need of 99 cheeseburgers, inflation approaches infinity, but you still only have 99 cheeseburgers.
When you talk about people hoarding Bitcoins, you conveniently gloss over the fact that people could just as well hoard gold and ammunition and canned goods and quality hand tools and clothing - And make no mistake, some people do, but most of us would rather just go about our daily business of living. Will some people hoard BTC? Yep. So what? Most won't.
Finally, you also need to consider the rate of deflation, vs the yield on reasonably safe investments. If you can make 8% investing vs deflation of 3%, only an idiot would choose to hold the currency instead of the investment.