There have been a number of great idea threads. The game supports many more variations than most players ever experience. This is one of my favorite threads..
Sitting on the Fence
One that might work well for your idea would be a tower map. Really tall but only wide enough for about 10 provinces. All nations would be placed specifically with the player at the bottom. You would have to fight thru them one at a time (hopefully) and see how far up the tower you can get in xx turns.
I have created a few AI challenges and run them. I remember D.A.R.E. (Deadly Atlantis, Rlyeh, Ermor alliance) Where Ermor was in the corner of the map behind multiple castles, and allied with a water nation on each side of it. The players all could only start on the upper half of the map far from the deadly AI alliance.
Another created a bunch of little AI nations which were all feeding Eaters of the Dead. You were in a push to try and take as many out as possible before they broke loose.