I don't think it's ever completely out of the question for the U.S. to get involved, and it's arguably more likely this time than any. But regardless, I agree with you that that chances of the U.S. actually getting involved are extremely miniscule. It's proxies will be left holding the bag, and the U.S. has no use to waste resources in a war it would lose, and save it's technology, manpower and aggression for it's imperial hold back home.