I thought about the Caliphate, but what put me off was the nonexistant immortal ruler thing and the fact that you get two provinces, one of which is wrong religion, plus you can only ever have Arabic culture. Having taken over the Mughals, I've just used Akbar plus an Excellent Minister to diplo-annex Gujarat and diplo-vassalise the Chagatai Khanate. I've beaten up the Uzbeks and plan to diplo-annex Nogai next on my way to racing the Russians to Siberia.