Now that Helldivers 2 is available on Xbox, a Halo crossover like what they did with Killzone is not out of the question. 
However, where Killzone got us 3 new primaries, 1 support weapon and 2 armors, I think the Halo crossover should give us 1 primary, 3 support weapons, and 2 armors, manufactured courtesy of Misriah Armory. 

It would mean the world if you read through it all and put your thoughts in the comments. 

By no means am I expecting any of these to be added to the game, but I tried my best to translate them into the Helldivers sandbox as faithfully and fairly as possible. 

Here’s what that could look like. 

Primary Weapons:
As cool it it would be to have them in Helldivers 2, Halo’s Assault rifle, Battle Rifle, SMG, and Shotguns are too mechanically similar to the Tenderizer, Defender, and Punisher. For this reason the only UNSC primary weapon that I think could be integrated well into the Helldivers’ armory is the DMR.

M392 DMR: 
This would be a marksman rifle and a sidegrade to the Diligence. To make up for its low magazine capacity of 15 rounds (same as the DCS), slow fire rate (180 rpm, or just over half that of the Diligence), and light armor penetration, the M392 would have good ergonomics and hit hard, dishing out 265 damage per shot. It would come with 5 spare magazines (75 rounds) and a 4x combat scope by default. 

DMR Breakpoints: Despite the light armor pen, the DMR’s raw power allows it to kill devastators and berserkers in two shots to the stomach, take off a devastator’s arm in one shot, take off a rocket dev’s rocket pods with one shot from the front (2 from the side), pop a brood/alpha commander’s head in two shots, and strip the limb armor from an overseer with one shot or the chest armor with two shots.

Support Weapons:
S7 Sniper Rifle:
 This would be a sidegrade to the AMR and Railgun, dishing out 600 ballistic damage per shot instead of the AMR’s 450 at level 4 armor penetration with a magazine of 4 rounds instead of the AMR’s seven and 5 spare magazines (25 rounds total) instead of the AMR’s six (50 rounds total). It would also have a fire rate of 74 rpm (compared to the AMR’s 400 rpm), a third-person crosshair, and a variable scope that can be set to 5x or 10x magnification. 
Its high damage would give it the ability to one-shot Hulks to the eye and two-shot Harvesters to the hip joints, which the AMR can’t do and the Railgun also can’t do without charging up. 
The AMR would outshine the S7 in ammo economy and clearing medium enemies, while the Railgun would outshine the S7 against Chargers and superheavies like Tanks and Bile Titans with its 1500 damage at full charge and level 5 armor penetration. 
 
M41 SPNKR: 
This would be a sidegrade to the Recoilless Rifle, boasting a two-round capacity before needing to be reloaded, but having 4 rockets in reserve (2 magazines) on a backpack instead of the RR’s 5 or the SPEAR’s 3. It would have HE and HEAT modes. On HEAT mode, the projectile does 3,000 damage at AP6 and the explosion does 150 at AP3. On HE, the projectile does 700 damage at AP5 and explosion does 800 at AP4. For both of these modes the projectile damage is slightly lower than that of the RR. 

MLRS-2 Hydra:
This is a handheld missile launcher with a capacity of 6 rockets with 24 in reserve (30 total) and rounds reload. It would be to the WASP what the Quasar Cannon is to the Recoilless Rifle: a slightly less powerful version that doesn’t require a backpack and has some unique features that differentiate it from similar weapons. 
In Halo Infinite, it has two firing modes: dumb-fire (which does slightly more damage) and lock-on (which is guided but does slightly less damage). The way this mechanic might translate to Helldivers 2 is with the projectile itself dealing more ballistic damage when locked on (500 ballistic, 200 explosive) and more explosive damage when dumb-fired (200 ballistic, 500 explosive). Ballistic damage would be AP6 and explosive damage would be AP3 (like the WASP). The explosion would have an inner radius of 3 meters, an outer radius of 6.5 meters, and shockwave radius of 7.5 meters (all of which are in-between the WASP & and Grenade Launcher)


Armor:
AP-9 Helljumper: Standard ODST armor like what you see in Halo 3: ODST. In Helldivers, it would have a new armor passive called “Ablative Plating,” which decreases damage taken from ballistic attacks by 33% (think Automaton lasers and Overseer plasma projectiles) and decreases enemy detection radius by 30% at night. 

AP-10 Daring: Light armor with the new Ablative Plating passive, styled after the armor worn by Veronica Dare in Halo 3: ODST. 


Possible outline for a Halo crossover