I've been making more progress with BletchMAME, not so much on the UX of the app itself but rather working with Mamedev to get the required hooks in MAME. I've actually implemented much of my hooks as a LUA plugin.

On Windows, BletchMAME is now distributed as an MSI, and in addition to installing BletchMAME itself it also installs the LUA plugins. The default configuration of BletchMAME instructs MAME to use both MAME's plugins directory as well as BletchMAME, facilitating the integration.

Long story short, we're making progress, but on the boring (and hard) stuff. I hope to pivot to more end user related functionality when I can get things working with off the shelf MAME.