ive been waiting for them to come out with a custom firefight/campaign mode where you choose were enimies spawn, when they spawn, what the objective is, what weapons you have, and what you need to do to finish it.
i know halo can be made this way (i used to mod maps on halo ce when bungie made ce which came out with many programers making scarabs and pelicans and even custom items) id love to see a game mode like that and i know it will be huge