My personal suggestion is that this would be a reskin of the Brass Beast - both are pretty bulky, and the Brass Beast has quite "tank"-related stats that fit this weapon's visuals quite well.

+1 Capture rate on wearer
Standing on objectives will grant mini-crits

-50% Max ammo capacity
Wearer cannot be overhealed

I could imagine this being an MvM reward for a new tour. It could be a guaranteed drop for your first completed tour.

Originally posted by Harrier Du Bois:

I could imagine this being an MvM reward for a new tour. It could be a guaranteed drop for your first completed tour.

I already suggested that, lol.

When deployed: Wearer is granted a 55% resistance to ALL incoming damage, and 75% crit resistance.
-50% less accurate
-25% Ammo capacity
-15% slower movement speed on wearer

It's the minigun you use when you want to be the tank (Get it?) for your team.
It even gives you half-a-chance against those pesky snipers.
However, in exchange, you're painfully ineffective at range, you can only carry 150 rounds of ammo limiting your capability to play independent of a dispenser, ammo pack or cart, and you're even slower than normal, not quite brass beast deployed slow, but still slow.

If this were to just be balanced around MvM and not PvP, then, hmm, maybe something like
+50% max primary ammo on wearer (less reliant on dispensers)
+20% damage vs bomb carriers
-50% damage vs tanks (other miniguns are -75% [ok technically its the tank with resistance not the miniguns with penalty but this is a for-fun hypothetical])
Giants will knock you away on contact (cannot bodyblock giants)
20% slower move speed on wearer
Projectile penetration upgrade allows penetration through tanks. (white text attribute)

Pros:

+ Fires Mini Rockets instead of Bullets
+ -100% Knockback while revved up
+ +15% Movement speed while revved up
+ +25% Damage against tanks

Cons:

- +40% Fire Rate penalty
- -75% max additive ammo
- No random crits
- Rockets do 60% less damage then their normal counterpart

I like the idea of this being like a team push weapon:

+20% damage resistance when revved.
+25 health restored on kill when under half health.
-40% holster speed.
+20% damage vulnerability when distant from teammates.

- fires explosive rounds
- 15% damage penalty
- +10% faster firing speed
- does mini crit damage instead of normal criticals
- +20% damage against tanks and sentry busters