ISIS/ISIL/IS would be far more likely to get “nuke” technology from the Pakistanis (who already have woking nuclear weapons) than from the Shi’ia Iranians.
I don’t disagree with your logic, but once this technology is out there, it’s basically going to be a free for all IMO. One group will need funds and they’ll sell parts of it. You may have a guy who isn’t as loyal to your group as you think. There are a number of ways this information spirals out of control once it’s provided for any terrorist group.