So far, there's no golden dome over the Vatican, but give it time....
That is true. I have read that one of the goals of Al-Qaeda was exactly that. To conquer the Vatican and to make it a giant mosque.
It is part of the Islamic religion to convert places of worship into mosques. It is a declaration of victory over foreign Gods.
For example if a Muslim army conquers an area with churches and synagogues, they will specifically with intent build a mosque on each of these locations, as a sign of conquest and victory. That is why they built a mosque on the Temple Mount in Jerusalem. It had nothing to do with Mohammed rising to heaven as the story goes. It was meant to be an overt symbol of Islam defeating the Jews. And so it is.
Muslims would love nothing more than to build a similar mosque over the Vatican. And they would if they could. The current Pope is a naive fool. Muslims only negotiate so called 'peace' as one of their many tactics of war. Muslims never know peace. They don't comprehend peace, even with each other. Their lives are constantly 'at war' with something/anything. It is a core part of their religion.