As we do not have the military nodes blog yet, there is very little we can say about military nodes.
We know that the election will be a PvP event. We also know that the delay in the military node blog is due to a change between the player actually fighting as their class and character to creating a champion you will fight as. Given that Ashes of Creation is not based around 1v1 PvP balance, the election system had to adapt or there would be classes that had a natural META advantage for being Military node Mayors.
At the present time we do not know what the military Unique Building is.
At the present time we do not know what the Military Metropolis Superpower is
Two additional side benefits of Military Nodes are:
From the 26 June 2020 livestream, we know Intrepid is planning on possibly changing the Bounty Hunter quest to include either all the Nodes that are allied with the Military Node, or all of the vassal nodes. We await further information.