What?
Oh, right. MacOS windowing layout.
Well no, the rom browser (and caching system these days) are far more user friendly for opening roms and giving information on which ones work well, etc.
Plus it puts something visual on the screen, which is always a plus.
And as far as I know the rom system is not an issue at all, besides the windowing toolkit bit.
I'm not really sure about the stage of the port with the rest of the emulator.
Of course, there's no reason one can't test it by compiling with GUI=NONE
But for that matter one could do ANOTHER GUI with a MacOS toolkit if they really wanted to.