Invasion model for the AI?

[Esoteric Paradigm]

I'm not sure that this invasion idea for the AI is really such a good idea at all.
England is very empty if you take out the AI. Invasions just fill up all the spare charters and it's just a mind numbing endless repeating cycle of kill some AI then invasion fills it up - there are simply way too few players to put in the parishes - most parishes either have no players at all or 1 player and AI ( sometimes razed after last invasion but in many cases not razed).

Wouldn't it be better to have an stronghold for each of the AI's that could be taken and defeated by the players?
The AI for each of the 3 could become stronger the closer to the stronghold we get, making it very difficult to defeat them but not impossible.
That way we could push the AI back and create safe areas because the AI would have a distance limit as to how far it's armies could go perhaps.

The world would end forever when the AI is finally defeated and a fresh world with random map would open up.