Very interested as well.
I have the 2019 new style Sierra 1500, 4x4, base model, 48,000kms (30k miles). Recall performed on the monitor last year, getting the same warning message to "service brake pad monitor system".
Took it to the dealer who sold it to me and has done all the work to date, but says I have 40%+ of the brake pads left. I am getting noise from the brake pads as if they need to be replaced, but maybe that's the sensor having worn down(?). Dealer said to come back in 10,000km and it'd be $1200 to change the pads/rotors on front and back (not sure why they'd need to change the rotors if the pads actually have that much life in them since pads are $100 for a pair and rotors are $130 each).
Also is there some kind of shortage of OEM brake pads/rotors? It took some work to find them, especially for the front.