For example? I'm not being snarky, I actually want to know, all we usually hear requested is cardinals/pagans/republics.
I'd say all of those are far higher on my list than a playable Pope, as they bring a lot more to potential gameplay than:
"King Whoever wants his excommunication lifted? Yes or no?"
"Some duke throws money at you for more piety"
"Some duke throws money at you for more piety"
"King Whoever still wants that excommunication lifted. Yes or no?"
"Sorry, decade until you can call for a new Crusade!"
"Some duke throws money at you for more piety"
"The Count of Orvietto has started the Independence Faction. It has 2.8% power, lolpoorbastard"
"Some duke throws money at you for more piety"
"You've lifted King Whoever's excommunication!"
"Duke Whatsit wants King Whoever excommunicated. Yes or no?"
It's, literally, one character (that PI has said before will never be playable, though I'm sure that isn't set in stone given the right ideas). I don't find the idea of granting nonstop divorces, papal indulgences, and tossing out the occasional excommunication to be super compelling gameplay, and its stuff that you'd have to deal with as a player Pope as all those events HAVE to go through your character. I can just see some snarky jackass now choosing to play the Pope in MP, and it taking 10 hours to get to 1067 as he keeps having to pause to deal with the silly amount of events thrown his way.