I would like to suggest one more thing:
An additional conversion of Co-Op maps to singleplayer ones, the missions are fun but they are unplayable if one doesn't have internet connection/someone to play it with.
I do realise that adding an AI option is practically out of the question, however simple conversion of ownership to one "house" would mostly do the trick, allowing the player to have some fun with those missions (I do realise that they are thought out to be played cooperatively, however it still is better to have them avaliable as additional SP missions than to not have them at all).