I find this discussion interesting. What platforms are desired? Can you provide more details about your proposed workflow and perhaps a simple but non-trial example graph? I am familiar with text adventures but not muds.

The simplest model I can think of is;

get (partial map) copy
edit copy
submit edited copy
a - conflicts detected, merge fails
b - no conflicts, edits are merged

otherwise you have to have a locking model;

browse map and select nodes to edit
lock nodes
edit nodes
unlock nodes

if you allow a person to lock a node and then lock another deadlocks are possible.