It'd be good to start a thread for Mod ideas (I can't create new posts ) .

I was thinking of doing a campaign mod based in a fictional Japanese/Chinese continent. There is an Evil Fish Demon trying to take over the world with his demon army. There would be big mountains in the middle where the oblivious gods live causing random disasters on a whim. You play the 'Japanese', 'Chinese' or evil forces. Alongside the humans are good and evil Demon units and individual units such as giant heroes/beasts that can be recruited or hired as mercenaries. The idea is to draw on the best bits from Chinese and Japanese Mythology and fiction to create a fun campaign and battle mod. Samurai zombies, huge wild eyed bearded demons, dragons, pig warriors etc.

Of course this all depends on the moddability of RTW units