Arabia will be formable as a culture union in 1.8.
Oh hell yes, best news of the week!
There's already a decision to "unify Islam" which is described as being "the caliphate."
Moreover it doesn't make sense to form "the caliphate" in this time period because there was a relatively well-recognized caliph during the entire period.
By the time you achive the prerequirements of the unify Islam, it's already game over for Ottomans...