A moving battlefield is something on my to-do list, although not a priority. Many years ago at BHP, Chronojam even had me create the geometry of a level for that.
The problem is such maps need constant QA testing and W3D Hub currently does not have the testing team size and attendance rate required to logistically pull off a level of such design scope.
Further more, in the time required to make such a map, I could create 5 other maps instead.
"Soft" mission objectives are the best thing I can do in a realistic time frame, such as those on Hostile Waters... Oh, and Fjord will have special objectives as well (not to mention quite a few secrets that will take you months to figure out!).