After quite a bit of labor I have gotten the beginnings of a 3D Map Editor for Mandate. As far as I am aware it doesn't require a significant amount of my new code so its possible that if I add features in the right order it could be easily ported to GAE.
I have, after lots of labor and annoying errors and unclear code, been able to allow proper placement of map objects in game, based on my previous faction build menu. I will be working on added all the other current map features later. I will be attempting to utilize the save feature, with some modifications for maps, to create a way to store a map. Since the map is effectively created in a game context, its requires both a tile set and a faction. I will try to make these option when I split map making into its own context activated from the menu. Currently and hopefully still after that change, you are able to place both any tile set object and any unit from the player faction. After the change ideally you could place a unit from any faction in the same tech tree.
This may or may not later be modified to include some sort of scenario editor. When and if I add the overworld map screen you should be able to use that as well in conjunction with the map editor. I haven't ironed out all the specifics yet.
Although this should be relatively easy to port to GAE it uses the UI library of GAE so I do not think it would be possible to add this functionality to MG or VG as well.