It’s a nice idea —/ but with a huge customer service issue.
The issue would be what if the DJ accidentally triggers the button lock without knowing it and without knowing how to unlock it? The forums and social media’s would be full of “help!!! My prime 4 locked up in the middle of gig” or even less helpfully “Prime 4 freeze mid gig”
I can though see the good idea behind the request though. Something like - hold down both shift buttons together for 5 seconds - the screen shows “locking - enter 4 digit lock code using channel cue buttons” … you would then press the headphone cue buttons on channel 4, then channel 1, then channel 2 then channel 3 to set a lock code of 4123. This would disable all buttons except both the shift buttons. When you return from the bar or toilet or girl etc then you press both shift buttons then press the headphone cue buttons in the right order.
As the prime 4 has so many USB ports you could even have a USB stick with a text file called “Unlocked” on it, and have a menu preset preference set so that the whole system is only operable while the usb stick with the “unlocked” names file on it. When you go to the toilet, take the usb stick with you, locking the unit, then when you return, plug the unlock stick back in