I don't believe it's possible in Call of duties. I would like for this to happen, but hear me out.
If you look at Halo 3, you see forge, and this is what you want to be able to do, but then look at the different items in the 2 games, they are totally different and Call of duty is a lot more complex. Halo 3 has such a small database of items. think about it, theres maybe 150 items in the game. Now look at Call of duty, you don't see the same item, and there isn't enough items in the first place. Halo 3 most of the things on forge are moveable, i mean the walls if you stand them there, you can run them over with a Warthog, in MW2 bricks laying on the ground can't be moved by a AC130 shooting down on it. Back to the items, theres maybe 5 of the same thing on every map on MW2, by this i mean things that you actually could place down. Theres the cars/trucks, red thanks and the long skinny tanks.
So i'll simply say this. Halo maps are made you could say "n***d" then they put "items" on it. Call of duty maps are made forming everything onto it, like giant caves on afghan or massive houses on estate. If COD make n***d maps and put items on it, they would be extremely boring maps will only flat different angled terrain with a few box houses on it.
This isn't a persuasive essay, I just got the drift you were trying to persuade us it's not possible. Not that I agree or disagree.
Making the program would be difficult enough to begin with. Especially if you are talking about a 3D editor. And caboose, when they said they would need a devkit, they where talking about real-time editing.