A blockchain removes the need for a trusted intermediary in financial transactions. It produces a financial system where nobody is in control. Banks are intermediaries. They won't relinquish control. So blockchains are of no use to them, but they keep trying to make their own version of bitcoin.
Adding quantum computing won't change anything. "… transactions can be even more secure and faster with increased encryption" but that's not useful because they're close to instant and perfectly secure already.
The Quantum Financial System doesn't exist. It's completely hypothetical and most of the descriptions of it out there were clearly written by people with wild imaginations.
For example, "The QFS is considered to be alive with a Quantum Benevolent Intelligence that interacts with each financial transaction anywhere in the world of finance, to ensure that it is; legal, owner-intended, and transparent."
https://inteldinarchronicles.blogspot.com/2018/12/the-qfs-and-gcr-are-golden-by-ron-giles.html