I'm also in favor of simplicity, but I think there is an increase in reliability from a microcontroller-based system over one built from discrete logic gates, a

I'm also in favor of simplicity, but I think there is an increase in reliability from a microcontroller-based system over one built from discrete logic gates, a mechanical timer, or electromechanical relays. I get that you might not want updatable firmware or might not want communications off the board, but you probably do want a microcontroller-based (with the associated firmware) machine.