Blinded cash issuers (using for example this system) and the bitcoin system could make a pretty good combination.  It could be similar to how private banks kept gold reserves and issued bank notes:

* Use bitcoin or a modified bitcoin/RPOW/bitgold like system to create a securely auditable, unforgeable, public, non-anonymous "high power money" analogous to gold.

* Issuers (or "banks") of securely anonymous (blinded) bank notes keep bitcoins as reserves.  By analyzing their public bitcoin chains, any customer can audit the reserves of any of these issuers.

Those who don't care about their privacy or who want to be issuers with trustworthy reserves can use bitcoins directly, while cash customers who like their privacy can use the securely anonymous blinded cash.   That forms a two-tier system, analogous to the old privately issued money system that involved mining and storing gold (bitcoins) and issuing bank notes backed by gold (anonymous cash backed by bitcoin reserves).

The whole system could be far more secure than the old gold-reserve + banknote system, because the "gold" is more difficult to steal but far easier to securely audit, and the "bank notes" far harder to counterfeit and (especially against modern investigation techniques) more difficult to trace/identify users.   The "gold window" for these banks could be far more secure from various threats than in the old private bank note issuers.  And it's all conveniently online.

So my take is to take advantage of the public and basically non-anonymous nature of bitcoin/RPOW type systems to securely audit people who claim to own X of them (such as currency issuers), while using blinded digital cash for transactions where privacy is more important than public audit.