I think it would definitely take a conversation between Takahashi and need to know personnel. His control might still be weak, but if we can we can entice them with some jutsu? (The ones Orochimaru gave us?)Honestly I don't think it's necessarily a bad thing that more people are aware of the potential of EM, as long as we are able to exert some form of influence on them. The Isanese were probably going to trade the jutsu away as they begin opening up, without our knowledge... and then what? This is probably a more favorable outcome than us not testing the jutsu, and in a year's time Hazō hearing of a strange weather event that froze everything around it, while the thread collectively shits its pants about someone having conducted the EM nuke test before we did.
I do think he's a rational actor. I think he would take the da gers quite seriously. Not sure what price or help he would need to enforce EM proliferation.