a problem is they they feel like their code contributions will not even be accepted for lack of shared goals. For example showing voting totals.
They're free to not run the upstream version but their own patched one. Not being willing to write code will certainly not make that feature landing any more likely.
Plugins in Rust are a whole can of worms, what with AOT compiling and static linking, you can't just monkey patch everything like in PHP. Essentially a plugin system would be a way to organise patches, to dependency inject admin-provided libraries instead of default implementations. Having a collection of patches should help designing such a thing, Personally I wouldn't even consider designing such a thing before it's clear what it will need to do, where it needs to provide hooks, also, that it will be used.