Probably what you said in your first sentence. At the time of manufacture, Z-80 CPU was the standard for controllers like that. In 2023, your first design pass

Probably what you said in your first sentence. At the time of manufacture, Z-80 CPU was the standard for controllers like that. In 2023, your first design pass would probably be an STM32 for real time control and possibly a PC as a UI, or a tablet if the UI needed to be portable. STM32 for real time control and a Linux SoM for GUI/database is a pretty common pattern used for industrial control these days.