I’m with you on the ODST DLC.
I would also like:
Flood DLC
Wildlife + inclement weather update
DLC that would expand the open-world with more areas and biomes
None-cannon Pirate DLC with magic shenanigans.
None-cannon Wizard DLC.
None-cannon what if the UNSC was the bad guys.
I would love to see the full game unlocked for $9.99 any more than that and I am taking my $800 on cosmetics and going to play Lost Ark.
Would love to see the return of the flood obviously, but down the line, i would definitely love to see us return to the Ark and meet with Red Team
Big story expansions on a yearly basis. Similar to how Destiny 2 does expansions.
For example adding 4-5 new missions in a new explorable area.
Classic weapon pack
Flood DLC
Scarab DLC
More wildlife and weather effects.
Prequal DLC Battle before start of the game.
Pavium & Voridus DLC
This type of game can have fantastic DLC but I don’t think we will get any as the focus will be the free to play multiplayer rubbish.
Mostly I’d like to have more stories of the notable characters in the universe. Not going so far as playing as the other characters but rather Chief being more of a rally point that these characters come to, to push back the Banished/Created/whoever.
Those I’d like to see would be:
What I expect:
Atriox DLC: Either fighting against him or as him
Endless DLC: them making these boys into a proper new enemy
Open World DLC: Them just adding more areas/HVT’s and so on.
Flood DLC: 1 vs 100, as it should be.
Alternate POV DLC’s: Basically they’ll do one for multiple Spartans I feel. Would just take place before or after what you’re doing on Zeta Halo. Different narrative, different story, same badass gameplay.
Arbiter DLC: Arbiter for whatever reason has to go down to Zeta Halo, then you get to play as him.
What I want:
Masterchief + The Weapon RomCom across Zeta Halo
Masterchief + Jega good cop bad cop movie flick
Rideable space rhinos
Saving Private Grunt (that Comms officer)
Music DLC (more customizable music and some classic tracks)
You know, you might be joking… but I’d love it if they did at least one of these for an April Fools Day event.
Edit:
The Fifth Element style story where Chief and his wacky Grunt sidekick have to protect an installation monitor from being abducted by the Banished.
Well the music DLC actually makes sense (343i finally dropping a Holiday album 
) but the rest would be fun content.
I ask the question, why so serious? Why does every single piece of content have to be in canon lore crafted by scholars and be blessed by Esports in order to be made? I would love to see more content that is on the wacky side. Stuff that breaks the monotony.
Rideable space rhinos I stand by 100%. Would be so cool 
I’d really like to see a real story not a prologue