Aside from the issue of whether there should be a Bitcoin central bank, OP puts the cart before the horse.

There can't be a Bitcoin central bank unless and until a large portion of Bitcoin transactions are done through Bitcoin banks.  I would estimate that portion is currently close to zero percent.

If we don't have widespread use of Bitcoin banks, a central bank can't regulate Bitcoin banks, it can't control Bitcoin bank lending or reserve ratios, it can't act as a lender of last resort to Bitcoin banks that don't exist.