Tim_the_Surveyor
Discussing this with my son brought out an interesting point. If I am allowed to cross Johnny, I could make hundreds of troops, move them towards the west to attack "our" enemy, only to break the treaty after I get set up the way I wanted. Yes, there is a 21 day break, but I could be so entrenched that Johnny couldn't possible build a defense in that time.
I know that this isn't necessarily what would happen but...
If a route is laid out for them to traverse, then you can control where the Frenemy can go and defenses can be build as a precaution/deterrence.
As for the Air Force, I was under the impression that one could fly in friendly air unmolested.
I think part of this would require you to be extremely careful to whom you granted this right. I understand what you're saying, but at some point, judgement has to come into play in the game. trust is a big factor with us in our alliance - all of us trusting one another implicitly, it didn't start out that way, and so that's a treaty that wouldn't be given lightly.