I always hope that during one of my SP campaigns, an AI faction will emerge as a contending power and once the world is plit between us we two could have a massive war...a few times it almost happended, but another failing of the AI is that it seems to not take measures to reduce the likelihood of civil war (or rebellions for that matter). The strong AI empires in my games usually crumble because of civil war.

A mod that gave the AI an income of florins (to make up for trade) and less chance for rebellion/revolt (to make up for mismanagement) might make the AI more competitive.