Use gource (Linux utility) to view the kernel source and hone in on relevant processors to see how the git source is being patched and upgraded. This technique will clearly show what companies are subcontracting and which companies have full time devs. The subcontractors will usually dump one or two pulls and disappear. Actual full time devs will continuously appear in the source visualization. The more people there are doing pulls the better, but there are usually not very many. This will also show what is dead and unlikely to change along with what it really means to have open source as you will see some of the leading maintainers pop in occasionally when they make changes with a broad scope.