I like the exploration in this area and I like all the above ideas.
From a different perspective, perhaps I care about isolation or viewing angles. In my mind, everything should be linked somehow but they could be compartmentalised or should be segregated between themselves. (This is regardless of sharing to other people.)
Having a knowledge space, I would like to utilise it everywhere, but I don’t want knowledge space to view the contents of other spaces. Like going to the library, knowledge are in their pure form; you won’t find anything personal there. (Unless you are the sneaky one who wants to date the one who read the same book 
). Good for public thinking or FR publishing.
At the same time, I would like other spaces to view the contents of the knowledge spaces (when connected), like bring notebooks to library, but the individual spaces can’t see how other spaces interact with knowledge space.
There is probably a few projects in workspaces. It would be great if they can be separated from each other, so there will be no chance to leak project specific information. Sub-space? If I have to create spaces for each project, there will be a lot of spaces.
I would like to have overview or personal perspective (space based or time based - not sure what’s better for me) where everything is linked and shared for my own evaluation but isolated from the other people/web.
For example, Project A links to Concept A, Project B links to Concept A.
Knowledge space / concepts should not see any projects.
Projects should not see other projects. (e.g. FR local graph)
Personal space should see everything.
Maybe the follow could work?
- Temporary access and single direction sharing
- Multi-spaces / space inheritance (Like Multi-type vs. inheritance)
PS. I hope I am not making it difficult for the team yet again 
PS2. This is why multiple obsidian vaults didn’t work for me.