I have to say, I’m not honestly all that concerned, at least as far as them presenting a nuclear threat. Having materials is one thing. Creating a viable nuclear weapon is another. It takes a lot of skill and technology to create a nuclear weapon. Perhaps a dirty bomb, but that wouldn’t be the end of the world (though it would certainly suck to be downwind!)
I AM however concerned with the potential for complete destabilization in the entire Middle East as a result of their actions.