Sounds more like a digital currency than a blockchain currency. When this is just between a few banks, which inherently trust each other, there's no need to build a sophisticated P2P blockchain for a job that can be done with a couple of SQL tables.
Do you have some quantifiable facts or sources to back this up?
If I'm going to repeat it I want to be certain of it.
That's not even taking into account the ransom banks pay for correspondent / agency banking and for SWIFT and the likes.
As well as the cost of liability of invalid/bad transfers, and banks oddly enough still "lose" money all the time, some of it is later recovered but virtually every time banks do account consolidation the books don't add up.
There are of course reasons for that, the major ones being the shared (and regulated) clearing system you're referring to (which I'm assuming this "bitcoin alternative" is aiming to replace) and then there's the fact that these are accredited financial institutions with reasonable controls in place to keep them honest.
In a hypothetical scenario where credit card authorization succeeds (meaning that the issuing bank is guaranteeing the funds to the merchant), merchant ships the goods but the funds don't make it to their account on the merchant bank side because the issuing bank "misrepresented the position" - if the issuing bank gets caught doing this they'll be in all sorts of trouble.
With a blockchain it becomes cheap to add a layer of ex-post verifiable mutual agreement between mostly-trusted parties.
My point however is that I highly doubt that it's the trust issues between financial institutions that is the primary driving force behind this implementation.
There was a real risk that solvent, multinationals (think Pfizer, or Nestle) would actually go bust because of liquidity issues, which could not be covered for a very short term.
The main reason was that banks didn't trust each other at all and interbank lending, without collateral, essentially went into a coma.
Not really...
I posted this before here on HN:
https://media.licdn.com/mpr/mpr/shrinknp_800_800/AAEAAQAAAAA...
You could have a "proof of stake" algorithm to power this proposed private blockchain, with the four originating banks (for example) given 25% "mining" power. The stakes could be readjusted when new banks come in, or existing ones leave.
What makes Bitcoin and other currencies expensive to run is that they run on "proof of work" algorithms, which are far more energy intensive, requiring huge amounts of electricity and specialised hardware. With proof of stake, you just need to show that you own a certain stake in the overall network, which is not energy expensive and quite feasible on a private blockchain.