Definitely. In that similar vein of thing, if for example I am King of France and the Duke of Barcelona is my vassal, and the Supemirate of Andalusia attacks me over Barcelonian lands, he should send me more troops since it's his very holdings that are at stage, or join me outright with his whole force. It's one thing that really bugs me that all this amounts to is a relations bonus in ck2 right now.
Something I similiarly would like to see is enticing vassals by promising them rewards. Such as "I will wage war for your claim on this county or duchy in exchange for you becoming my vassal" kind of thing. This could come in both "I will be the agressor for your claim" and "I pledge you X amount of gold and troops for you to wage your own war" kind of thing.
I also hope their "Clans/Tribes have to depend on relations, Feudals on definite contracts" design don't go too far. I don't like the idea of relations not mattering as much in a character/relation driven game. I mostly like the way feudals function in ck2 right now, but I can see how the "super bad relations mean no levies at all" mechanic might be too, well, unfeudal. But I would still like relations to matter to the point where the rule would be "you always get X amount of troops from this vassal, but you might get more if you're better liked, or if it's in his interests, or his troops might have higher morale, or he might send more professional troops (especially if they're changing troops into "peasant rabble levies", "pro military men-at-arms", and "knight characters"). Or you know, if they really hate your guts, their troops might be "late", like the Great Late Lord Walder Frey's at the Battle of the Trident, to use an entirely historical example.