A sizeable amount of users had taken to using Reset or Power+Select to exit any application because they didn't know our emulators had menus or that they could be exited in any other fashion. Reset is very not-recommended because it can cause file corruption, and Power+Select doesn't allow the emulator to exit and save your emulated battery-backed RAM.
We also have had a few threads here, and confused people on IRC who were like "what key is it to exit emulators on the GCW Zero?", assuming that this existed already. When told that the emulators had different menu hotkeys because of different unused buttons from the respective emulated system lacking that button (for example, L+R in OhBoy, only L in FCEUX, Select in Picodrive, Start+Select in PocketSNES because all buttons are used, Y in ReGBA...), they were instead just hopelessly confused and some asked for this unification as well.
Manuals are also inaccessible during gameplay, unless they're also online.
So yes, there was, and still is, a case for unification. "Emulators can all be brought to their menu with Power, or one or two other combination(s) that make(/s) sense for the emulated system in question" is much easier to remember for a user, much less error-prone, and much more satisfying.
Plus, who knows if an adult wants to hand the GCW Zero over to a child while travelling in a car... Or plenty of other uses where remembering a single thing is better.
The Power flick standard is already implemented in some emulators. It works this way:
--> If you press Y while Power is raised, you will take a screenshot of the game, and you will not enter the menu.
--> If you press nothing while Power is raised, you will enter the menu. You can then take a screenshot of the menu, if you so desire (for keeping track of settings or posting them online), with Power+Y.