Consider stable coin, for example

A fiat bank might want to collect stablecoin fees from prequalified stablecoin users.  Pre-qualified stable coin users are restricted to a closed set of actions they use to robotically operate their fiat accounts.  The fiat banks know all paths, a priori.

So, the banks sign up to the notary protocols, the protocol that publish the honest amount of fiat outstanding. The entire loop is closed and under pipeline control, notaries on duty.  

All we need is a personal user contract for stablecoin, simple enough with the new cards and escrow system. The fiat bank in charge of sign ups, collect more fees.  Central banks should support the concept.