In Civilization games you can trade maps like currency with the other players.  I'd like to (eventually) see that in LH.  That would be one more thing for diplomacy.

In the last game I finished (not won, just finished), Resoln showed up on my factions list when she started casting the spell of making.  And there was nothing I could do about it because I didn't know where she was.  I mean, I did pay everyone I could to declare war on her, but it apparently wasn't enough.  She finished the spell without me ever even finding her borders.  If I could have found her, I maybe could have done something.  I at least could have attacked her because I could cast Arcane Monolith near her, Cloud Walk to to the monolith, and then hoof it the rest of the way (I play Mancers, who move faster, so I actually could have made it; custom faction).  

That particular situation aside, I think that map trading would just add something to diplomacy.