1. i dont like non-retaliation cluase. If you getting your ass kicked you have a right to fight back.Somewhat related to the topic.
I like a lot the concept of Cold War - which is neither Peace or proper War, but something in between - implemented by Amplitude in Endless Legend and probably some other games.
By default two nations start in Cold War, which means:
1. You can enter their territory, but they can attack you without declaring war on you. You cannot while you're there; you need DoW for that.
2. You both can attack each other in neutral territory, without DoW.
2. Interesting idea. Could work.