As to MP map naming issues, I see 2 possible solutions.
First option. (a spin off of the who owns more cities/Pop. idea)
Since all MP players will be on the same Base Map, with un-named features, the first player, despite Team, that reaches, or pushes back the FoW on said map feature, gets to put up a unique name if one does not exisit. Despite a Rivers length, they have but 1 name, from origin to the Ocean, so no naming "my piece" of this river stuff.
Since the naming of terrian objects among Team mates could be confusing, and since all players will start with the same "Base Map", what if when you select a teammates game ID, form a pull down perhaps, your map instantly changes all named features to what they have currently name those items. Consider it a layered drawing of tha map, with each having a Layer to name on and when the Gamer ID is selected, that layer is revealed to the player who selected it.
So you would have a basic 4v4 player Map. Your team consists of Dave, Marie, Bob and Samuel, your Dave.
Dave has named the Central moutain range "Albacore Pass"
Marie has named the Central moutain range "Witchata Spine"
So when Marie selects Dave's gamer ID she see her Central moutain range name change to "Albacore Pass".
When the player leaves the Player selection Pull down, their own map layer is restored. I suspect that is what the XML usage would probably do....