There should be more campaign styled multiplayer maps, where you have neutral villages, who support you with units or ressources after you conquered them or which you can plunder. This would give the maps a new taste. Maybe you can even raise the amount of players up to 12, so that those factions can be added even to 8 player-games.
This would make the multiplayer games feel more like campaigns and would make the gameplay more immersive and diplomatic, since you have neutral factions.