More options in Custom Games, and in turn, more options for Customs hosts and Action Sack. That’s it.
Apart from that, there’s no competitive reason for any of them to exist, except for Armor Abilities. Loadouts hurt the “equal starts” philosophy (even moreso with Halo 4’s multiple passives and out-of-match customization), and Ordnances increases the randomness of a match due to how players can accumulate points, and not know when or who will drop an semi-random “care package”.
Armor Abilities fit perfectly into what we can see for the design of Halo Infinite, giving players intuitive and skillful options for each engagement, and increasing the skill ceiling while keeping the skill floor relatively stable. Slope hops, while having been a thing since the Bungie titles, are a part of this “empowerment of choice” philosophy as well. Easy to understand, hard to master. Since sprint has sliding as a supplemental mechanic, other Armor Abilities such as Jetpacks and Evade can benefit from multi-button mechanics as well in the form of a double-jump, aim hover, ground pound, or spartan charge. Despite their controversial nature of increasing the skill floor, these multi-button mechanics would give players more options while still being relatively simple to use. It also helps that the maps we have seen so far are designed in such a way that having Armor Abilities wouldn’t hurt combat pacing too much, similar to how sprint doesn’t even hurt pacing at all.
I don’t care if Armor Abilities, Loadouts, and Ordnances are part of a seasonal update or new title, but I do care about giving players more options to play how they want, and the subtitle of Infinite for a free-to-play live-service game on a proprietary engine gives me some hope that overhauls are possible. Halo’s popularity in the early console multiplayer era was partly built on Forge and customized game modes. 343 should empower the players even more than they already have, and it wouldn’t hurt to try.