My idea is to create simplified map editor as a layers. Player could create as many plan layers as they need. Additionally, our simplified map editor will deliver simply drawing tools.
Why?
Many players asked for example to change build improvements behavior to allow build by action points, like in Civilization: Call To Power 2. Thanks to plan layers, player could set cities position, tile improvements, etc., before He/She build it.
Drawing tools could be used to plan military strategy. Also, it could be fun if players can share own plans, by sending them to allies.