I think sooner or later there will be an official plugin/theme store/marketplace/hub. All really good pieces of software have one: Sublime Text -> Package Control, Android -> Play, rust -> cargo, nodejs -> npm… the Roam community is building Roam Depot.
I think currently this should not be the focus of the devs because RemNote is still in pre-release. The API is not declared stable yet. It is also a bit like the hen-egg problem: No plugins -> no store, no store -> less incentive for developers.
In the past a package repo were sometimes community efforts (Package Control, Roam Depot).
Here is what we (as a community) can do:
- Curate plugins and themes on a low-overhead community-managed list like awesome-remnote.
- Later, when the number of plugins grows: Build a simple website with easy install (One-click install plugins) with search, categories and maybe rating.
Regarding the distinction official/non-official: I think the term is “featured”. These are small examples implemented by the devs or exceptionally well done plugins by the community (like the graph view) for which the devs took time to add them to the plugin page. I think in general both plugins and CSS will be mostly developed by the communtiy and the devs working on builtin features and maybe assisting with important plugins.