I’d be disappointed if Firefight came back exactly as it was in ODST and Reach. Maybe they could make it like a massive war with 30 or so Spartans (the players), Marines and ODST’s against bots? Who wouldn’t want to play this game mode at least once? They could have Scarab boss fights and loads of vehicles for players and enemies to use.
I’ve dubbed the idea: Skirmish, a great mix of multiplayer action against bots with story to the missions.
It would be less like fighting enemy waves over and over like Horde mode from other games and more like an all out war seen in Battlefield 4. No waves of enemies with set numbers to kill, just a nonstop battle. You want shelter and quiet? Get into your base where it’s safe. There would be objectives like saving stranded marines, disabling anti-air Wraiths and players could have the ability to call in extra backup or be able to request weapon drops from a Pelican. It could be about base defense but also with some thrown in offense objectives that require a full assault on the enemies base. Like a Scarab tank that players have to board so they can destroy it.
Maybe we could even pilot a Pelican to transport marines and other players to locations on the map? There could be maybe even more players at once to allow stuff like player brought reinforcements instead of just friendly AI bringing a Warthog to you. If the campaign is going to feature more squad command type stuff then maybe we could order friendly marines to attack, retreat/regroup, defend the base, follow my lead, etc. All the objectives are meant to aid you in defeating the enemy once they are completed.
Ultimately, you can win by defeating the “boss enemy” or by completely destroying the entire enemy base, which is heavily fortified. Some maps require you to beat the end boss to win. You can lose by eventually running out of respawns or having your base generator destroyed. Bosses can vary: Multiple Scarabs, monolithic Forerunner constructs, legendary Brute Chieftains (think Tartarus) with personal bodyguards, etc.
The idea is to make you feel like you are in a massive battle with chaos and destruction everywhere and you aren’t alone. Playing with friends would be a blast. “Hey, Kevin! Can you deliver a tank to us? We really need one!” -Joe…“Roger, I’m heading over in a Pelican but you guys need to be careful because that’s our last Scorpion.” -Kevin.
Who knows how that little story I made up will end 
Maybe they’ll run out of tanks and have to do something crazy like hijack a Wraith. The possibilities are endless and you’ll be bragging to all the interbwebz that your Skirmish Squad is a force of nature.
These maps would have to be immense so they would get their own unique ones. Here’s a few ideas on some maps.
Strife- Battle the Covenant and Promethean armies in the frozen terrain of Installation 05 where plasma burns become the least of your worries once a blinding blizzard strikes the area. Awaken an ancient Forerunner war machine under the fields of ice and put an end to its extinction agenda.
“ONI says there’s something big underground, thaw out the ice and find out what it is.” - Sarah Palmer, UNSC Infinity
Example of what this map could look like
Arcadia- Fight to avenge the civilian casualties of Pirth City among it’s fresh ruins and its undamaged districts. If too many civilians die, the mission is a failure. Spartans are the first responders to the attack so in the first few minutes you won’t have any marines to help you. Try diverting some of your team early on to escort VIP’s to evac zones to ensure their safety, then focus on reclaiming the war-torn city.
“The trails of Pirth run red with the blood of the unworthy…” - Jul 'Mdama, Storm Covenant
Example of what to base this mission off of.
Crusade- Raid the holy cities of Sanghelios and eliminate the Sangheili Terrorist Jul 'Mdama to break the Storm Covenant’s hold of the planet. This mission will require an immense offensive effort, but beware, enemy squads have been ordered to infiltrate your base and cut off your supply of reinforcements.
“Jul wants to hide deep within a bunker with his personal guards and wait for his troops to cut off UNSC reinforcements. Show him that Spartans aren’t to be tested with hiding…” - Captain Lasky, UNSC Infinity
Example of what you’ll look like between matches 
Feel free to tell me what you think and if you have any ideas for a map, let me know!
