This is the most spot on post ever. The amount of stuff in the world that relies on old, tried and true "a file appears in a directory somewhere overnight and is processed the next morning on 'the other side'" method is probably staggering. But most people nowadays don't know or understand this at all, as they've never been exposed to this. And why would they ever be. And all the fixed column width stuff as well and delimiter based import/exports.
Heck I've had to fix one of these things where it suddenly started failing the overnight transfers and when I went to check why it was because a fricking musician had named their song to include the delimiter used in one of those...
Yes, it's a complex problem. Yes, mythical man month, etc. But US banks over the last several years have averaged a quarter trillion dollars per year in profit.
They just have very little incentive to change things. In the meantime, they're earning interest on funds.
An ACH transaction is literally FTP and text files. If you can find a way to get rid of millions of lines of COBOL you can probably disrupt this.