@wjt that's a great question. I think it's a blog post size answer, which I'll do today. Thanks for the inspiration!
I have a personal interest in this because:
a) I have zero interest in being a distro packager in the classical sense of "maintaining packaging for apps I don't otherwise develop", except when necessary for, uh, my job working on a distro
b) I have ended up responsible for a fair few apps on Flathub for which I am not an upstream developer
My solution is automation – chiefly https://github.com/flathub/flatpak-external-data-checker – but that's a plaster, not a real solution.
Server run by the main developers of the project It is not focused on any particular niche interest - everyone is welcome as long as you follow our code of conduct!