But Iran would not target Mecca and Medina -- they would target Riyadh or Jeddah
The Islamicists would indeed hit Israel, trying to target Israel’s coastal plain, main population center called the “Dan Bloc” (from the Biblical Tribe of Dan).
They have already stated that if they hit Israel’s Arab population centers then those Muslims will be considered honorable “Shahids” or martyrs.
So they don’t care about the Dome of the Rock or Temple Mount. Those places are run by Israel and in cooperation with Jordan.