Now, I know I'm late to the party and new mission nodes being added is old news by now, but there is a side effect to that and with the possibility of The New War adding even more nodes, I thought it was worth discussing. Each time new nodes are added, Arbitrations are locked again. To my knowledge, this has happened two times so far.
I don't even play Arbitrations, but I think anyone that's unlocked them when the amount of mission nodes was X shouldn't have to unlock them again by completing X amount of nodes + whatever amount of new nodes were added. Accessibility to them should be grandfathered to everyone that's already unlocked previously, new nodes shouldn't affect that.