In the post Made a Reviung5 macropad I briefly mentioned that there's no built-in support for the Reviung5 in ZMK. Since I had to make it work anyway, I decided to spend some extra time and contribute it back to the main repo.
It took some time to get the local build pipeline of ZMK up and running, but it wasn't too complex. Then I had to make changes to the shield definition to make it match other keyboards in the repo, and opened a pull request.
After a few requested changes, it's been finally merged!
It's not perfect - I don't have any LEDs on my Reviung5, so the support for those simply isn't there. But now if someone else comes along wanting to make this keeb, they can simply generate the firmware from the CLI tool in a few minutes and won't have to fiddle with the more complex definitions.