With Islam (supposedly) originally seen as the last Branch of Christianity, what if he instead promoted a Mohemmedic Christianity - or Bedouin Christianity, but with Mohammed kneeling to the Emperor of Rome as a Christian Leader, and setting himself up as the "Patriarch of Mecca", but still leading the Caliphate (or I suppose the Patriarchate ITTL) as an independent Christian state that was pro-Roman.
What would be the consequences?
So we have 6 Patriarchs, (Rome, Constantinople, Alexandria, Jerusalem, Antioch and now the contentious Mecca).
A united Arabian polity, that is steadily converting itself, but refuses to invade fellow Christians, even if they are Misguided.
My first obvious instinct would be a Persia-Screw, but I was curious as to what would happen.