Think skatepark editor from the Tony Hawk Pro Skater series. How fun would that be to have a level editor for Splinter Cell? You would be able to choose from a handful of location types.
-Public Place (mall, monument, town square, etc)
-Etc, etc, etc.
From here, you would be able to choose different textures such as wood, metals, cement. Within the borders of the level you would be able to build walls, air ducts, catwalks, offices, stairs, zip lines, ladders, etc.
Anyways, it'd be a fun thing to play around with and they could throw official competitions for best level design. A man can dream can't he? Haha. Feel free to leave your thoughts, and I apologize if this has been brought up before.