I worked on a payment system using the UK's Faster Payment Scheme a while ago. The SLA for latency is two seconds end-to-end, and is usually much faster than that, was simple enough for a gang of underpaid COBOL programmers to implement it successfully, and didn't have a mechanical error rate worth bothering about. In January it moved 186.1 million payments and 161 billion pounds:

http://www.fasterpayments.org.uk/statistics

FPS is UK-only, but there's nothing about the technology or the commercial and legal machinery that wouldn't work internationally. If SWIFT is really as bad as you say, it could be replaced with a better instance of the same technology; it doesn't require a haunted git repository to fix it.