Those are all good questions. I’m inclined to think that keeping this as simple as possible and following similar principles to the existing moderation environment would help make this useful while not creating too much extra work for moderators or admins, as both groups already seem overworked. I think this will already be complicated enough to begin with (for instance, how will communities in other instances be handled?) and fraught with potential for conflicts (for instance, include or not include communities of certain political slants?), so care should be taken to keep this somewhat minimalistic.

With that in mind, here are some possible concepts to consider:

Moderation: following the principle that Lemmy/Piefed allows moderation by users (through blocking users, communities, and instances), community mods (through removing posts and banning users), and instance admins (through overseeing mods and defederating or default blocking other instances), in that order, how about if the users themselves were the first (and perhaps only) ones to decide and control which lower-level communities they want to see structured in their feed and how? It seems to me that community mods should only be able to moderate their own community at each level, and not be able to moderate posts from levels below.

Creation and use of taxonomies: should the creation of the taxonomy be the job of users, community mods, or instance admins? I’m inclined to think that this should also ultimately be left to users to determine, but there could be a mechanism that allows anyone to share/publish a taxonomy that they find useful (or perhaps branches of a taxonomy, like Gaming), and allow other users to either import or subscribe the taxonomy or branches that they like, from a list of different available ones that have been shared/published. Admins could then have the option of setting entire taxonomies or a group of branches as defaults for users of their instances. This would allow users the freedom to create the structure that they would like to see while also allowing others to benefit from that work and not have to duplicate it, and finally also allowing for different competing structures to exist. Community mods could informally ask creators/maintainers of taxonomies or branches to include their communities in that structure. To add communities to a structure, there could be a simple button in each community that said something like “add to structure”.

I think that doing things this way would allow the most freedom, flexibility, and utility, while also minimizing additional work for mods and admins, as well as any potential for conflicts. Another factor to consider would be how much impact would this kind of thing have on resource utilization of instances?

I hope this all makes sense and helps provide some ideas for how this could work.