Here is a neat thing

 A box with a couple of processors.

But the box is sealed. It is in a Faraday cage. It has self destruct, tamper resistant explosives. Since it is locked, unavailable, use spectre proofed unknowable processors. The NSA cannot complain.

Then the buyer of the box gets some set of public keys it can distribute to clients who can proof the box at any time, for a congestion fee. Load the box with the new sandbox code, giving it a Fedwire interface, CB to CB on entry and exit. Inside this runs a variety of codes, from Swift, Viper and Solidify and others. Fiat banks buy these boxes, pay the telecom fees and open a variety of provable contracts, its and pure liquidity to their clients. The internet for Fedwire networks.