Yep, multi map option in editor would be really good.  This topic has been brought up before and I don't think Frogboy ruled it out completely yet.  Many have asked about this in relation to undrground/above ground adventuring, multi-planes of exitstence, etc.  It would also be nice for indoor adventures(ancient abandoned temples to explore, haunted houses, etc.)  So some of the alternates maps could be very small in size to super huge.  Maybe you could post some other core features you would like to see in a map editor strager?  For many of us, having access to multi-map option is right up there towards the top of wants or needs for the game. 

Oh this would be a great feature, though I was under the impression this was already possible (modding only). But if not already a feature yes please please make it available it will add such great depth to RP style Modes. (thinks under water world with Merfolk, and Sharks) or Outer Plane area with Deadly Slaads. I have so many ideas that I tried to do in AoW or Nwn and was never able to do well due to game Engine limitations and my well less then stellar modding skills and terrible coding and scripting.

Definately a feature I would love to see.

Would also love to have the ability to load one map from another, and have the states of the maps be saved (even if the AI basically 'pauses' on the map you leave) while keeping at least the sovereign's details persistant between map loads.

Could see that being exceptionally handy for creating various dungeon 'sub' maps.