Since the UNSC is in a war with Insurrectionists before the start of the Human-Covenant War and the insurrectionists are still around, I think it’d be a cool idea to see a firefight mode where the Spartans have to fight against an invading force of Insurrectionists with stolen UNSC vehicles. It’d be a cool way to possibly fight multiple Scorpions and Mantises (or Manti, whatever the plural for Mantis is) to make it challenging.
Possibly rogue Spartan IVs as well! I can complete my Marine kill commendations if this was implemented O_O