cue light system, half duple serial over long distance and power over the wire

Quote
You could do half-duplex, I have an example here:

Gammon Forum : Electronics : Microprocessors : RS485 communications

You send a query, switch back to listen for a result. This could be done multiple times a second (eg. "turn LED 4 on, are any buttons pressed?").

thanks this together with some phantom power circuit or POE could do the trick.

any ideas?

If you go this route, you might need over voltage protection. since LTC1480 might be uncomfortable with short to 44 and 57 volts DC. Here is the plans;-

Plan A.
Dia Surge Suppressor Discharge Gas Tube

Plan B.
Clamping diode

Plan C.
Catcher diode

Plan D.
Zener diode

Plan E.
Metal Oxide Varistor

Plan F.
Multi-layer varistor

Plan G.
TVS diode

Plan H.
TVS IC

I am sure this list could be very long. I just started.