@Frank_fjs the 4 button games are an easy fix on a supergun. A bit trickier if your cab is strickly JAMMA (3 button).
But they don't require additional hardware compared to analog games etc.
Also there does exist a version of Action Fighter using digital controls on S16B. I just need to decrypt it first then it's only the matter of updating 1 ROM.
At the end there should be only 6 games requiring extra hardware: