The next nuclear use as a weapon will probably be by a small group with a very good cause, unless governments start cleaning up their acts.
It is almost impossible for the marginal and fringe groups to obtain or assemble nuclear weapons. It needs advanced technological know-how in several sectors. That is why less than 10 nations own nuclear weapons right now. But then, I am worried by the possession of nuclear weapons by countries such as Pakistan and North Korea. No one can predict what the rulers of these countries will do in the future.
Perhaps the greatest limiter on the proliferation of nukes is the limited interest among the general public in astronomy, ironically the one thing that would make nuclear proliferation less dangerous... /