That's a good idea.
If they go over to China or Iran, at least they stand in stark contrast to our allies. If we have any anymore.
See, the thing about Goliath, even those who like him will not tell him he is wrong. They fear that petulant little swat before he realizes he's wrong.
That's why we have not heard from the rest of the Anglosphere. They know we are on the road to destruction...and they are afraid of both the outcome and being the first one to say it.
This is the kind of thing that sounds good in theory and is said by people (in this case Trump) who probably haven't actually considered or understand the ramifications.
Pakistan is not going to give up their nuclear weapons any time soon. Period. They won't because of their historic rivalry with India - which is somewhat unrelated to the GWOT. If Trump put that policy into effect he would immediately throw Pakistan firmly and entirely into the Chinese and Iranian sphere of influence. We'd be leaving them no other option.
It is one thing to threaten to withhold aid over their support of terrorist groups and lack of cooperation with us in the war on terror. That is something they can actually rectify - or at least improve. But demanding they dismantle their nukes is a bridge so far beyond the possible that Trump might as well just say he is suspending all aid to Pakistan. This would mean immediately writing off basing special forces in Pakistan, no overflight rights, no intelligence sharing (much of it behind the scenes), no vital sea link to truck supplies to our forces in Afghanistan, etc.
One can agree or disagree with aid to Pakistan based on their poor record of dealing with terrorists, but the nuclear weapons issue is not really the determining factor of whether we send them cash.