Public and decentralized are not necessarily the same thing. Even if just two other banks join in, under an equal footing of ownership of the proof of work, its no longer centralized. I think assuming "all blockchain tech must be used only for situations with anonymous participants" is unimaginative gatekeeping. There is plenty of room to reimagine business process workflows between consenting participants, that doesnt at all hinder the public coin marketplace, or infringe or harm principled stands trying to change the world. These arent coins a single human bank customer would ever hold or use, these are for institutional settlement.

A good example could be a construction project where the general and all the subs collaborate on a database, but no one company owns it.

The smart part of JP Morgan's plan here is scalability. It might be centralized now, but it can be trivially extended into becoming decentralized at the flick of a switch, without a redesign.

Microsoft already has pushed for a non-public-anonymous-participant private blockchain that has throughput of around 1600 transactions per second. https://medium.com/coinmonks/coco-framework-a-game-changer-i...