I like Varoufakis, and I don't hold Bitcoins, but I didn't find that article particularly insightful. It's just the old Keynesian fear of deflation - which invariably uses the Great Depression, since there's very little evidence of the supposed harms of deflation besides it - and a fair criticism of Bitcoin being currently more driven by speculators than regular users, but with no explanation why that's an insurmountable flaw in Bitcoin.