So this is not just for quick favourites but also for cutsom menus?
I made a suggesting for something about this but for the sidebar or in your case looks like a custom editor, not sure if the Devs like the idea or not but i do hope if you can take a look at it and see if it can be combined with your proposal to be a more elegant solution…
as you know Blender sidebar suffers a lot from too much addons that are put there with no regard to the clutter & the scrolling they add.
looking forward for your project to be a great success, Good Luck.