I believe dperfect is asking why a blockchain is technically necessary for this. Why can't the large banks cut out the clearing houses by dealing with each other directly?
Is this really about the blockchain technology, or is it more about political cover to push for big changes in how business is done, eliminating legacy systems and killing some industries currently providing services to banks?
What does it mean to fake a transaction?
What does it mean to verify a transaction? With Bitcoin it's possible to do because the balances are public. But once you start making transactions private that deal not in value that exists on chain, but are merely promises for some externally held value, then who can verify its legitimacy?
By providing a common ledger that can be used when you desire single entry bookkeeping you don't necessarily need all the backchecking as you're using a smart contract to ensure upfront that when the money is settled the assets move.
>> It takes some financial assets 3-5 days to settle
That 1-5 days to settle isn't due to slow and disconnected systems though, which is what many looking from a tech perspective believe. Most financial transactions are matched in settlement systems the same day they are traded. The 3-5 days is for prefunding of underlying accounts, tear ups and other asset class idiosyncratic reasons.
There is little trust between organizations. Both from ethical and technical perspectives, I wouldn't trust anyone to run a central clearing database for anything. I spent 10 years in the finance industry, overconfidence caused by incompetence is the hallmark of engineers in finance.
Blockchain solves this problem by letting everyone participate in the infrastructure, and to violate the legal and ethical agreements, a majority of parties would need to collude.