you're absolutely welcome to submit a PR
Ha. Actually before posting this thread I did go through some of the code to see if I couldn't just develop a small patch for private use, but
You'll find that the UI is, as of right now, too deeply ingrained into the MAME core to be easily removed.
Indeed. And if experienced devs are wise enough to not mess with it, then inexperienced ones like me are pretty much guaranteed to break things on all kinds of levels.
And hate on RetroArch all you want, but there's one thing they're doing right, and that's their modern, modular approach - and their lack of a hierarchy keeping things stagnant.