MIDI panels and devices supporting MIDI are very common in the broadcast industry, and Just Macros has support for MIDI. In this video a MIDI panel is used to control both the ATEM audio faders, but also a set of DMX lights.
And ADLINK make a set of cards that have relay contact closure outputs and digital input sensors. These GPI/O functions can be very useful when building broadcast systems.
Using the Black Magic ATEM CCU from Just Macros is then briefly covered in this video.