Bitcoin, the volatile digital currency, cannot help the Greeks of today. But it could mean a great deal to those caught up in currency crises to come.

Greece’s fundamental problem is that it cannot work its way out of its financial hole the way just about every other country outside the eurozone would: by printing money, and in the process making its goods and labor cheaper. With a freeze on transfers of funds out of the country and a daily limit on how many euros Greeks can withdraw from the bank, there is a very real threat...