I just had three more ideas:
a map without any stone
a map with up to 16 players
a challenge map where the AI should have trading outposts, not headquarters again
Funny : I uploaded an 8 player map recently that has few stones (a couple of rocks and place for 1 mine halfway to your first opponent), and I wanted to try it in FFA with AI with trading outpost.
I played yesterday a game on an other map where I gave the IA trading outpost, I think it's a good idea.
As for new ideas, what about these one :
The logistic nightmare. seafaring map (or not but it popped in my head as one) where you HAVE TO have shitty building placement. No medium or big spots near your mines (coal /) iron/ gold are far away from another, all big and medium spots far away from eachother and generally speaking inconvenient spot placement, no way to make straight roads, only way to attack opponent is through a choke, such things.
No big spot would aslo be an idea, but I don't know how to make sure you cann't steal any from the defeated opponent. Except if you make a map where you cann't attack, only defend (seems tricky but might be faisable), you can adjust how long you have to defend with an artifact or territorial win condition (just puting the lat artifact behind a more or less huge wall of stones or sth like that). Well, I let the idea in the air, but I just realised that other tribes (I have to try other tribes than barbarians more seriously :p ) have training buildings that fit on medium spots. Might not be balanced ! then again, if it's to play against AI, it doesn't necessarely have to be balanced.
I thought of a vegetarian or vegan challenge, but it seems quite complicated. For barbarians (all tribes?) it means no upgrade and for some other it means no seafaring right? Maybe I'll try to think of a vegan tribe Plus I think gamekeeper can produce animals out of thin air, right ? (they don't need pre-existing animals on the map contrary to fish breeders iirc)
That was it for now, I'll think of other ideas.