I think the idea of Fedcoin is very interesting, and this article does a good job of highlighting what it would mean in taxonomic terms.

My biggest unknown, and the problem I've seen with the idea of a centrally managed cryptocurrency (especially one with convertibility) is the creation/redemption mechanism. The proposals I've seen talk about varying the block reward, or having some sort of transaction type that can only be submitted by the central bank.

I hate to think, though, that the entirety of the security of a nation's money lies in the ability of the central bank to safeguard its private keys. Bitcoin's monetary policy is deterministic and consensus-based, so it's not really vulnerable to this.

It's all well and good to talk about CBCCs in the abstract, but the technical challenges involved are non-trivial and shouldn't be glossed over.