I think you should be able to put ai on a map so that you can make your own campaing mission, add your own story or how you think it should have ended like in halo reach were everyone died exept jun, that made me so mad because everyone sacrificed themselves exept him, so you could make a mission were you play as jun and you are on the pelican with doctor halsey when you start getting attacked by elites and you crash, then you try to find help and on the way jun dies but doctor halsey keeps running and on the way she finds master chief(wich i know is so limited but you never know) and he saves her.
To make the AI so advanced they could work on any map with ease no matter where they are placed would take a whole bunch of work for 343.
You are talking about campaign forge? I say no. too expensive. I would rather have a smooth running game.
However, it would be possible to add firefight forge. With placeable flood spawn points. Flood knows where you are anyway.