Very simple:
-A Halo Reach style progression/rank system, maybe have Halo 3 skill implemented in it too.
-The progression system should reward armor and visors, no filler like emblems and charms.
-Battepasses should be shelved and any armor pieces within them can be implemented into the progression system. Even store armor should transferred over to the progression system as well.
-The game needs a defib and focus should not be on microtransaction anymore and instead about giving players a reason to stay and play like most past multiplayer Halos did successfully.