In general i'd like -Less adhearnce to 3-path symmetrical layouts -More organic natural landcapes, less blocky angular layouts and structures -More vertical tiers/overlooks
For particulars (not really good ideas, but this is what comes to mind) -Something forested and outdoorsy in the vein of the cabin map from MW2 or the waterfall/canyon map from MW1. Not a remake like studio, but something inspiried by those maps -Shopping Mall....like one of the really big ones with multiple tiers and ammusement parks in the middle. -Honestly i kinda like what they did with Mob of the dead, and wish they had a MP verison of Alcatraz.
For the uneducated, it's a massive castle with ****loads of rooms, hidden passageways, huge outdoor areas (the map would be large, not medium or small), and the ground isn't even all the way around so it'd make for slightly interesting terrain as well.