I was not sure where to put it and I already spent some time on writing this up, so decided that may as well post it here, maybe it will be of some use to someone. So, here goes nothing
(I did not put any numbers in, because those are up to actual designers to decide, not to some rando like me)
Desperado
Uses one-handed glaives or two-handed glaive(it’s about time, Blizzard, I want big ole glaives), because creating a new weapon type is a bit unnecessary, IMO
Still has Fel rush and Vengeful Retreat, because those are cool.
You got three guns - two pistols, rifle and Demon Cannon, used for the most powerful abilities. Both pistols and rifles have limited magazines, starting to recharge after the bullets are completely depleted. Without bullets the abilities associated with a specific weapon type can still be used, but extremely inefficient. Switching weapons is automatic on using specific skills, but by depleting both magazines at once you will run into the situation of both your main “magic schools” being useless while reloading.
Demon Cannon is used for powerful abilities and does not have a magazine, but requires a lenghty cast to charge the weapon, which can be offset by overcharging it with certain passive and active abilities. Demon Cannon is primarily used with overcharging. Overcharge has a decent duration and you can hold several charges, but every charge over one eats away at your body, as demonic energy starts to overflow.
Apart from the magazines, you possess a Rage, which is slowly gained by using abilities. Rage allows you to instantly recharge one of your magazines, overcharge your Cannon or get emergency healing in a desperate situation. It takes several full magazines to charge your Rage, not too fast.
Pistols(Demon Bullet causes abilities to ricochet to other enemies nearby). Able to move while casting and channelling
Fel bullet - Fire several shots, consuming a bullet.Demon Bullet - inflicts Bleed. If enemy is affected by Demon Burn, consume the Burn and amplify the Bleed, based on the remaining Burn damage
Suppressing fire - Channelling. Continuously fire into your target, dealing heavy damage and applying slow. Demon Bullet - Attack all enemies in range
Die Demon Die - Heavy damage shot, usable only on enemies below 20% HP or with Demon Bullet.
Probably choice talents or sharing cooldown
Double the hatred(Major cooldown) - Fire from both of your guns simultaneously, doubling the output of every ability, until the magazine is emptied
Back to basics(Major cooldown) - Replace your pistol abilities with Annihilation, gaining an amount of uses based on the bullets. Demon Bullets are replaced with Death Sweep charges
Guns are disposable(Medium Cooldown) - cast away your pistols, emptying the magazine and dealing damage to your target and enemies around it, based on remaining bullets and leaving behind a damaging zone, as your demonic weapons explode with violent force. Replace with But Hunt is eternal after cast.
But Hunt is eternal - Short Cast. Charge towards your target, dealing damage and rooting them in place. Reload your pistols and gain a Demon Bullet for the pistol.
Return fire - Consume Demon Bullet from your pistol magazine and charge away from your target, setting yourself at 25 yard distance from it. Apply Hunted to the target.
Rifle(Demon Bullet causes abilities to explode with shrapnel, dealing damage in small radius and applying dot effect).
Straight shot - Fire a bullet, dealing damage to all enemies in its way. Demon Bullet causes the shot to return back after reaching its maximum range
Fel Firestarter - low damage shot, applying heavy Burn. If an enemy is affected by Demon Burn, spread it to nearby enemies, alongside with the Burn, applied by the ability. Demon Bullet increases the Burn duration
Fight or flight - Large cone and range attack, dealing damage, knocking out and applying bleed and slow. Slow and bleed becomes stronger with distance, damage and knockback is strongest in close range. Demon Bullet creates an allied Demon Hunter, casting the ability from the opposite direction after a short delay
Loaded for the Pit Lord(Medium Cooldown) - Your next rifle shot gets the benefit of Demon Bullet and applies Hunted to your target.
Turret - place your rifle as turret, firing at enemies in range, emptying the magazine. Its lifetime is based on remaining bullets. Turret fires Straight shot at enemies, its damage increased for every Demon Bullet consumed
Cannon(powerful abilities, require overload to be casted efficiently)
Hellfire Shell - Powerful single target shot, exploding into firestorm on impact. Apply Hunted to the target.
Spew Demonfire - Continuous stream of fel flame, applying burn and slowing down enemies. Activating this ability dispels all your DoT effect, becoming stronger for every DoT dispelled
Misguided Missile - Launch the rapidly moving rocket, dealing damage to enemies it passes. Activate again to explode the rocket, dealing heavy damage. Can be activated again to teleport to its location, disorienting surrounding enemies
Gun Devil(Major Cooldown) - Transform into the ultimate living weapon, reloading all your weapons with Demon Bullets and drastically reducing the reload time for them for the duration. While the ability is active, you can charge Cannon while moving and using other abilities, including other Cannon abilities.
Rearm(Rage ability) - Instantly reload your depleted magazine, guaranteeing at least one Demon Bullet.
Refuel(Rage ability) - Get an Overload stack
Replenish(Rage ability) - Heal for a portion of your health
Fortified Flesh - Defensive cooldown, reducing damage taken and giving you a free cast of Return Fire.
Passives:
Cycle of vengeance - Using abilities of different weapons gives stacks of haste buff, lose stacks every time using abilities of the same weapon
Wounded prey - All your cannon abilities leave a Demon Burn on the enemy, dealing damage and increasing your move speed in radius of the target. If distance to your enemy exceeds 30 yards, gain a short burst of speed with cooldown.
Hunted - Can only have one Hunted enemy at the time. Hunted enemy always gets the secondary benefits of Demon Bullet on shots fired against it(such as ricochet and shrapnel). Hunted lasts for medium to short time.
Fel Metal Jacket - Your next Demon Bullet deals increased damage and changes the last bullet in your magazine for one of the weapons into Demon bullet. Every bullet spent has a% chance to give you a stack, chance increased with stacks of Cycle of vengeance.
I need Moarg bullets - After emptying the magazine of one of the weapons, gain a stack of Fel metal Jacket
I need bigger guns - After emptying your handguns or rifle magazine, overcharge your Demon Cannon, allowing you to fire it instantly on full charge
Big guns never tire - using overcharged Demon Cannon reduces cooldown of your Gun Devil ability and heals for a small amount.
Destructive tendencies - When your DoT ends, an explosion of fel flame occurs, granting you rage and dealing damage in a small radius.
Keep your enemies close - Range on most of your abilities is 30 yards. While you are or was in previous 5 seconds closer than 15 yards to your target, deal increased damage to them.