With kingdoms I've been thinking about how M2TW could be improved, and using CAE as a base here is what I would do:
Map
Fix america so it lines up right (so Britain is opposite New York, not Florida )
Remove the Atlantic as a territory (it is, this is how the uncrossable sea is achieved).
Allow all ships to cross the Atlanic (the vikings were there in the early 1000s so why not everyone else) this would mean that the AI would go there
Factions
Remove Kawarzem (it does nothing... ever!)
Add Norway, Maya and the Apachalian tribes
Replace the Russian Principalities with Novgorod (they look better, Lithuania look the same... half the time i though Lithuanian agents were mine )
Units
Replace the roster for KoJ, the Teutonic order, Lithuania, Aztecs, Byzantium, Egypt and the Seljuk turks.
Give the Mesoamericans the ability to build canoes as there first boats, and if they destroy 4 European boats they can build their own. (as the Apache can with guns and boats)
Random
ZoR for Crusader Kingdom knights and units.. in antioch you can build Antioch kights, in Edessa you can build Edessan guard etc etc
the Crusader Order guilds should be able to build the full rosters of there order... (so if you can get a Hospitalier headquarters you can get hospilater gunners)
Just my thoughts, i might add more.
I posted this here cause i love this mod, and i would use this mod as a basis for my improvements