With a POD after the Middle Ages, the challenge is to get a resurgence in the Coptic Church in Egypt, to the extent that 30%+ of the Egyptian population is Coptic Christian by the modern day.
My best idea is that Muslim leaders try to promote religious Muslim nationalism in Egypt by trashing the pagan and Christian history, including the pyramids etc. Coptic Christianity thus becomes seen as the true Egyptian identity that many flock to once nationalism arrives.
Thoughts?