Your quote states that when war breaks out, the weapons would be mounted on the host countries planes. Which again means control rests with the host country. My quote comes from the second paragraph, in the main summary.
As for a nuclear deterrence pact, sure, the US could back out - and therefore shatter all other deterrence pacts while allowing a nuclear weapon to be used offensively with no devastating consequences. Not going to happen.
America categorically would not encourage other nations to build weapons. Why would it do that?
I don't think more nuclear states is a good thing. What I know is that disarmament isn't happening, and that there is an astounding incentive to secure nuclear weapons regardless of their legality. I also know that their stigma is causing hundreds of thousands of deaths. Between Iraq and the sanctions of Iran, how many have died? And for what? To ensure that Iran never had a chance to never use a nuke to murder-suicide Saudi Arabia? Come on.