-——I bet Iran will eventually threaten to nuke Mecca -——
No, certainly not. That statement indicates misunderstanding of the big picture.
The goal of the Iranian mullahs is control of Mecca and thus Islam. Israel is a side show and really irrelevant. Saudi Arabia and Mecca and thus all of the Arabian peninsula is the objective.
Back about 1979 a contingent of armed Iranian troops flew in to Jeddah for the hajj and attempted to capture the Grand Mosque. They were wiped out by Saudi Security forces, every man killed. The objective remains the same but the method has changed.
The Iranians are not totally stupid, they could given time find fissile material that could be traced back in some fashion as being from the USA, they could IMHO very much attempt an attack upon Mecca, maybe an aborted but successful detonation nearby or just the discovery, just what it would take to awaken all the latent moderate Moslems in America.
All the world believes its a CIA attempt and thus like throwing rocks at your neighbors hornets nest above his open window who will the hornets attack?