The new 8th ed rule book complete with new FAQ's already out- who would have thunk it.
There must be a new Sheriff in Nottingham.
There is a section in the new rule book that that that talks about using a GM. To many this may seem like a new concept but actually the concept of a rule judge goes waaaaaay back. Long ago before recorded history ;p -miniatures were used to to teach tactics. Students (Players) would move the troops around and a Judge (GM) would tell them the outcome of their decisions.
The Use of a GM to Ref a war game used to be standard back in early editions of Warhammer and 40K. In fact it is mentioned as the norm in the original Rogue trader. It has simply fallen out of fashion. At least till now.
In my old gaming group (I'm talking 4th ed WH here) we almost always used a GM. It seemed to make the game run better. It also made any night where we had an odd number of players less awkward.
I always liked being the GM for my group. I enjoyed the ability to control the situation and make up interesting scenarios and be able to modify them on the fly to keep the game going. this was the same in RPGs as well as tabletop Wargames.
Recently, the Warboss sent me a link to a some GM tropes called "Grand Tabletop Rules List" I felt that many apply to both Tabletop wargames and Roleplaying games. Enjoy them as they are pretty funny.