I believe it would be reasonable to make a major alteration to the forge, since this is a new trilogy in the Halo series. The previous elements of forge would be included; however, perhaps an editable camping-like mode would be included in Halo 4. A campaign-size map would be somewhat ridiculous, but another map like Forge World could possibly do the trick. In this forge one could not only edit map and objective structure, but also create AI players which would behave according to given qualities, objective, and the actions of the player. I'm not suggesting to make unparalleled super tactical AI's, but maybe just give them the commands to defend objectives, kill enemy team, evade, etc. One could give them special traits, specific behavior, a certain appearance, some restrictions, or even some speech or subtitles. I know it all sounds crazy, but just think about it.