Although this isn't possible to add into the game since we don't have the source code, if this was ever added I bet it would be very useful for map makers.
So, the idea is a grass tool. When making realistic maps, you want to have grass all over the place and not just in patches in random places. Placing the objects takes quite a while to do for an entire map.
But the grass tool would be in another little tab or whatever of Map Maker, and from there you could pick a color and draw over the map in spots you want the grass or whatever to be with options to change the size of the brush and stuff. Then, there would be a dropdown menu of all the objects you have (Like in the object tab of Map Maker) and you could choose one. Next, you would change the pitch, roll, yaw, and stuff and the size of the mesh, with the "Is Large" and "Randomize Clone" and all of that stuff there too. Then, click OK and voila, where you drew with the brush now has grass in it's place. You could do another color and draw for other objects as well. (The color doesn't show up, it just tells the game where to place the grass/obhects). Or, maybe it could work similar to a terrainmask/heightmap kinda thing.
I'm pretty bad at describing, I hope you guys can somewhat understand what I said XD I just think this would be a useful tool for lazy map makers, although it would be very hard to put into the game.
So uh... I guess what do you guys think or any other ideas for the tool? I'm sorry if this idea's kinda bad.. *slowly goes to hide behind chair* o3o