I would love it to be lass “arborescent” in its structure.

Reminds me of this post where I said :

The things we refer to as “threads” are actually “branches of a tree”. […] It would be useful if a discussion branch was not only shaped like a thread, but also had the usefulness of one : sewing, or tying together different discussion topics.

This post was about the “Comment/response toward post.”. I also like your "Posts toward users. ". Coauthoring is definitely valuable ! Relatedly, one could imagine a channel (like on Peertube) owned by several users. Then the channel could publish their common work.