It shouldn't be necessary either. The proof-of-work is only necessary to avoid a central party wrt. which blockchain is the "right one". Financial institutions are working together with each other, they can easily just agree on which blockchain to follow. But without proof-of-work, the blockchain is just a database with atomic updates. I don't see why they would need a blockchain for that.

Ripping Bitcoin in two gives you two fairly uninteresting things: 1) hash-cash and 2) a database full of public keys/signatures. Only combining the two gives you something interesting: negotiable/fungible hash cash (hash cash that can be transferred from person to person via a distributed database).