AAs:
Add some new options and tweak the existing ones. Let the Hardlight Shield use a pistol-class weapon if the player has one so he’s not totally defenseless, but remove scope or charge shot when used in this way. If testing proves this is a little -too- useful, reduce the shield’s duration or damage absorption and see how that goes. Give the Thruster Pack some more range or at least the ability to use it twice before recharge, or combine it with the Jet Pack and make a Jump Jet AA where the player shoots upwards and in the direction their stick is pointed so they get this sort of arcing super-jump thing. Make Active Camouflage (plus maybe Armor Lock or a new AA of some kind) the equivalent of a “power” AA, you can pick it up off an ordnance and use it, but once it’s used you swap back to your armor’s standard one. All AAs have a distinct visual signal on the armor such as a field generator on the Hardlight Shield’s forearm or the visible pack on the Jet Pack, allowing reconnaissance work to identify player AAs for their teammates.
Ordnance:
Map ordnance works functionally in the same way Halo CE-3 spawns did: weapons drop in set locations at set intervals. Personal ordnance should drop the player’s starting loadout weapon (to refill ammo/swap with a picked up map weapon), two grenades of the player’s choice (selected on loadout), and either the speed boost, overshield or damage boost powerups (random, but priority given to one of the player’s choice).
Loadouts:
Allow one automatic weapon and one mid-range precision weapon (BR, CC, mid-range equivalent to LR) from each tech type (Human/Covenant/Forerunner) as selectable options, and allow the player to choose from the three pistols as sidearms. Players start with 2x frag, but can select what their ordnance drops for them and get others off the map/dead enemies. Players get their choice of standard-level AA and can give one of the three powerups priority (effectively: when one is selected, it has a 50% chance of being dropped, while the other two have a 25% chance). Steamline tactical/support package options to be thematic to character playstyles (Grenadier allows 3x grenades of each type to be carried and reduces explosive damage taken from indirect hits, Stealth as it is, et cetera).
Weapons:
Boltshot now functions like a two-shot mauler. Long range precision weapons (DMR, LR, Needle Rifle) spawn on maps like other weapons such as Needler and SAW do. Remove aim assist and magnetism from hitscan weapons. Add “emergency” automatic weapons (Plasma Rifle, SMG, Forerunner equivalent) that aren’t very effective but are dropped more regularly and in more places than other weapons. Grenades shot in midair or on the ground explode instantly. Weapons possess weapon bloom in unscoped fire to reduce spam accuracy, replace with gun jump (see Halo 4 BR) in scoped fire modes.
I have a few more ideas, but these three categories IMO speak about the larger concerns of most players that Bungie hasn’t already addressed like the lack of close-range maps.
EDIT: To clarify on the concept of “Power AAs”, these would be in map ordnance much like how oldschool equipment and powerups spawned on the map.