Implementation of Blockchain in banks is said to be the new trend now. My question is: Would the private blockchain be kept private in a bank or will it be shared among a group of banks (or even possibly among all the banks)?
In the later case, is there no confidentiality issue, since a bank can know the transactions which are done by its competitors or its competitor's clients?
Think of a blockchain-based implementation of the financial backbone as the modern-day equivalent of Automated Clearing House (ACH), the national standard for processing checks.
Based on banking documents and blockchain organizations focusing on blockchain-based solutions for the commercial banking sector the solution will be a permission-ed, national-level blockchain with each participating bank being allowed access to the network. In this affect each bank would also be a miner with no reward, just confirming the transactions are valid.
The matter of confidentiality will be determined by the customers, and will pick their method of banking accordingly.
This would depend on the use case for which the bank built the blockchain. In some cases, it might be for using internally, but other cases may require it to be shared between a group of trusted institutions, customers, and regulatory agencies. Still other cases would require the bank to share the blockchain publicly, perhaps restricting it to a "read only" mode.
Banks are experimenting with the technology, but that doesn't mean they have yet figured out how (or if) they will use it. Private blockchains still have questionable use cases, and bank-created public blockchains still have questionable legality.
This answer might also be of interest to you: Why are banks and other centralized entities interested in block chains?
