I think we will not see a return of Spartan Ops for various reasons. So we could see the return of Firefight in the Next Halo. Here are some ideas I had that should be fairly easy to implement. Please check out the video and share your thoughts.
All enemies: Flood, Covenant, Promethean.
New Game modes: Firefight Extraction, Firefight Fortify
Map editor?
Unlockables: Achievements, Armor, Voices