Will Christians be able to pray in the mosques of Morocco, Saudi Arabia, Iran or Kuwait?" demanded one contributor to a Catholic website. "Muslims should practise what they preach!" And what about Jews wishing to pray at the holiest site in Judism, the Temple Mount? Pigs will fly before the Muslims allow that. That's not to say it might not happen one day soon, but if it does it won't be because the Muslims "allowed" it.
I suspect every city in Europe has a "former mosque" site somewhere...