“ThreadGroups”
Sorry for bumping up this thread again, but I woke up this morning and couldn’t rid myself of the idea that Groups could be used for defining scope of concurrency as well. The concept of PlaneGroups perhaps would work also for ThreadGroups?
I didn’t analyse this very deeply, but at first thought it seems to me that Planes and Threads shares some data conflict risks - because the basic problem with a Plane is that of conflicting threads - one must restrict the scope of a Plane’s influence. In short, GH definitions must be “Plane Safe”, as well as Thread Safe.
Which is what lead to the idea that Groups could be a way to manage also thread safety. With the additional benefit of making the scope of separated threads visible.
Threads being one of them? 
// Rolf