FYI the reason there is no priority on multi-system talkgroup scan is that it takes too long to figure out if there is traffic on a channel to do priority monitoring. To do priority, it requires the radio switch to the other channel and check for activity, then switch back to the current channel if none without punching too big a hole in the audio. The time it would take to sample a trunked channel for activity would take long enough so as to make large gaps in the audio that are unacceptable. Conventional channels and monitoring a single trunked system are OK, that can be done quickly enough to not make the audio stutter too badly.
Historically, Motorola has always hated priority scan, and viewed it as a "dirty compromise". Their solution was always to use a completely separate receiver monitoring the priority channel and overriding the non-priority audio if the priority receiver went off. I have an old Mocat State-Police model CB that has a second channel 9 priority receiver in it, even
. If you look at some of the old repeater and base station designs, they always had a space left for a second receiver, usually for that purpose.
Some of the mobiles had that option, too. It was IIRC called a "Hot Red Receiver" (HRR) option.
