Just chiming in a bit..
Rob, it might be interesting to old geezers like me as well as newbies entering the field to get a perspective on Plan 9 and its evolution. The motivations behind it. What your group was trying to accomplish, the approach, pitfalls and the entire decision making process as things went along. Even things that went horribly wrong and what happened etc.
Sorry for my potential ignorance here, but other than the documents that come with the source code distribution, there does not seem to be any official textbook style document available with that level of detail going into the evolution and back story.
I am thinking more in terms of the multics book that came out after that project failed.
Perhaps even some college level tutorial videos on YouTube that do a deep dive. Leaving your group's collective wisdom and insight for prosperity. Anatomy of a Research Operating System. Approaching the Design of a modern day distributed Operating Systems, practices and pitfalls.
(You can stop laughing 😃 now....)