You'd be right if you thought that just using for an append-only log doesn't seem like a big difference. But the key thing to note is that they said it could re

You'd be right if you thought that just using for an append-only log doesn't seem like a big difference. But the key thing to note is that they said it could replace CLS, the current settlement system which makes sure the net direction of monies is paid out. So I believe this to mean that instead of using CLS to settle up with currency transfers like USD or EUR, the banks agreed for certain subset of trades they are willing to agree on how to value Bitcoin, or some other crypto, versus the currencies they trade, and then settle the trades by periodic, usually daily, Bitcoin transfers. If Bitcoin's value isn't stable, then it would be risky for these banks to hold a lot of it in order to settle trades. Perhaps this is what would sink this usage of the blockchain, but probably only a quant would be able to answer that. I did find it somewhat amusing that the article claims a benefit of real-time visibility of settlement status. I believe some settlement systems still work by sending csv files over ftp (+ssh / sftp).