Think that any country with a functioning nuclear power infrastructure is within a few months of a nuclear weapon. The technology is well documented by now, so Japan, Germany, Taiwan and Brazil are surely nuclear capable entities,
Meanwhile, if the Iranians see their co religionists getting slaughtered in Yemen, they are not likely to remain passive, any more than the Turks were when the Cypriots declared Enosis and union with Greece.
Unfortunately, the US has trained the Iranian military to adjust to the US way of warfare in Syria and Iraq, so I do not see any easy pickings in any actual confrontation.
Separately, if memory serves, there was a provocative Adelphi Paper about 20 years back by an Arab author which argued that nuclear weapons proliferation would serve as a stabilizer in interstate relations, especially in the Middle East.
I do not think the author was prescient enough to consider the emergence of non state actors such as Al Qaeda, which perhaps erodes the thesis.