GDPR regulation is being overlooked. No large North American or European bank conducting transfers using cleartext blockchains will be able to meet regulatory requirements.
"Laws such as Gramm-Leach-Bliley, HIPAA, and COPA in USA and GDPR in Europe mandate the use of encryption, along with other tools and processes, to protect citizens from unauthorized parties such criminals, unauthorized commercial interests, foreign governments, etc. ..." -Zooko
Current transfer systems Fedwire, SWIFT, and ACH conduct transfers privately. Why would the upgrade to blockchain technology necessitate removal of longstanding regulatory and privacy primitives?
"The Zcash protocol’s cutting edge use of zero-knowledge succinct non-interactive arguments of knowledge (“zk-SNARKS” or “zero-knowledge proofs”) makes it a truly innovative privacy coin that offers confidentiality for peer-to-peer transactions similar to those afforded to fiat currency transfers (e.g., ACH , FedWire, SWIFT, etc.)." -Eric Winer
Regulated 1st-world banks do not advertise their transactions in the daily newspaper. Why would these same banks wish to publish transfers on the Internet, publicly and permanently, in real-time?
In the field of Information Security is the concept of "data aggregation". Public transactions on their own have little value. However, once multiple data sources are compiled and matched, the data becomes meaningful, and vulnerable to exploitation.
Chainalysis and CipherTrace are two such companies that specialize in this type of blockchain-to-customer data aggregation.
Banking regulators (will) view vulnerability to such attacks as a gross violation of the multiple regulatory standards mentioned above.
JPM is testing zk-SNARKS (used in Zcash) and ING Bank is testing bulletproofs (used in Monero and Grin). The privacy age is upon us. However, such technologies won't be viewed as privacy coins for long. Encrypted blockchains will be viewed as standard operating procedure.
Just as no bank would dream of using HTTP over HTTPS, no bank will rely on unencrypted blockchains.