What steps should 343 take to sustain population?

I’m curious as to what the community feels 343 can do to keep future Halo’s population steady like Halo 3’s. I personally think we would need an addicting ranking system, desirable unlocks, lots of game modes at launch and finally, a new huge feature to market. For Halo 5 we had warzone, the most we really had for Halo 4 was the disastrous flood gamemode and Spartan Ops, Halo Reach had the HUGE Forge World as well as Invasion and Head Hunter (everyone at the time was hyped for that), Halo 3 had Forge and Theatre, etc.

Feel free to use the population thread.