This would be a solve all to late game large map micro management -
I always loved being able to turn some of my cities over to the ai, it worked great in Romance of the Three Kingdoms - another great example is the Hearts of Iron series where one can simply drag a box over the desired units/territory and select if you want them offensive/defensive/buildup & such (Perhaps it would require a champion to designate as leader for each area you wanted under ai control -
Could have an option to turn your Sov into ai - making your entire faction under ai control for those that just want to watch for a while, or could have just this city and maybe that one under human control with the other 7 controlled by one or more champions for you "Tiberius Longloins, keeper of the northern portion of our territories has sacked the Tarth city of York Sire, shall we add this new conclave to his jurisdiction?"
I don't know how much it would take to implement this but it would really be neat to sit back & watch my Empire that I"ve spent the last 1000 turns building do mop up for me