The feature you first suggested was actually the RTW "Provincial Campaign", a feature that was unfortunately never included. Adding factions that are not in the actual mod would not work, but if we were to create a new map for the provincial campaigns it may well be worth the effort.

Also, Florence has been merged with Genoa and Milan to create an "Italians" faction. I would rather not turn any of these states into rebels.

Thanks for the suggestions,
SR