No wonder the maintainer of Karabiner ( https://pqrs.org/osx/karabiner/ ), one of the most powerful keyboard customizer on OSX, had to start rewriting it from scratch for macOS. Maybe the underlaying keyboard/accessibility APIs in macOS have changed so much it forced a rewrite.

If that's the case then I'm starting to see the macOS major release policy as being as conservative as possible. I.e. no introduction of unnecessary changes unless it warrants advancements in hardware integration.