The idea is simple.
A Event like CoD zombies but in a different way. 4 Spartans in one group fight against the flood.
the event kicks off with a global transmission that a flood outbreak occurred on multiple locations. The players task is to fight against the flood in a horde like game type but with a community goal. If the community fails the flood grows stronger . The next time the flood will have a much more coordinated behavior because the gravemind grows stronger. For a bit more objective players get the option to complete random task like “secure a landing zone” to unlock a new spawn location for other players or to gain access to orbital air strikes.
it’s just an idea not even for release but some time down the road.