Consistent UI for users and great UI APIs for plugin devs would be a nice perk.
I have a couple of nvim plugins in flight and building the UI has been the hardest part so far. (A couple of examples: https://imgur.com/a/RZV2eYJ )
We want to create interfaces to make this simpler for people to use.
One example is here: https://github.com/mjlbach/neovim-ui which is just in a separate repo to make it easier to work on rather than one huge PR.
This is an extension of the ideas that I started in https://github.com/nvim-lua/popup.nvim and a few other places.
The idea would to be to create interfaces that users, plugins and/or GUIs could override to provide a unified experience while still being customizable for users.
(and as a self plug, I think we have a lot of interesting ideas in telescope.nvim about UI that could be upstreamed over time)