As my longer article shows (http://papers.ssrn.com/sol3/papers.cfm?abstract_id=2424516) these are two separate questions. The really interesting one is whether the protocol/decentralized public ledger/blockchain could be a valuable innovation--interesting because I see the possibility of having a serious debate over this and perhaps of curing some of the defects I've raised. The uninteresting one is whether bitcoin can be a general purpose currency--anything's possible but that really seems to be about a close to zero probability event.