If you add canbus support, having the capability to switch on outputs via can data would be the way to go. Look at the Lingenfelter canr-002 for idea's. Extra points if we could gnd an input & have it send a can command, could be used for AC request or changing throttle map on gm ecu.
I have an e38/t43 in my vy ute which means I needed to remove the ac wire to from ecm to a separate switch & the same for the reverse lights. All the stuff on the market has silly pricing for doing 1 thing.
i.e can relay for reverse is $275usd. https://www.speartech.com/product_p/6lr ... trelay.htm