Indeed. But inside a deflationary economy, it is impossible for banks to make money off of deposits by lending them to someone else. So I dare say that banks cannot remain solvent with BTCs, the economics don't make sense.

That said, plenty of people are "banking" with online BTC wallets. Instawallet, Coinbase, etc. etc. The economics for these services work against them, and they are hopelessly doomed to failure.