I agree with Camerlengo completely! Sovereign of Papacy should be current Pope.
Also, I love the idea of clerics in catholic nations going through some process of becoming cardinals. and the Pope to be elected from the class of cardinals. Each step of improvement should carry other title, for example bishop, archbishop, cardinal instead of receiving stars like in KOH1. Same with the orthodox countries and similar with Muslim nations.
I would also entertain the idea of giving a royal court members some specific titles or roles in addition of them being marshals, merchants etc.
Lets say King can name his most experienced and trusted marshal "Commander of the Royal Army", "Chief of the Royal High Command" or "Chief of the Royal Guard". Similarly, most experienced and trusted merchant could be "Chancellor of the Royal Treasury".