Here's one I was toying around with:
Nuclear Plasma Shotgun
Unique
Clip size: 12 (uses 3 per shot)
damage: 8d3 (same as Plasma Shotgun)
Alternate Reload: Overload the reactor, causing a nuclear explosion.
Description: Like all nuclear weapons, this one replenishes it's own ammo as time passes. Can't be manually reloaded. The regular plasma shotgun is an exotic, while this is a unqiue, so I think that'd make up for it's improved usefulness.
Also, Looking at the exotics and uniques list, I realize that there's exactly ONE melee unique, the butchers cleaver, and no melee exotics. This is bothersome because exotics were implemented precisely to combat the aggravating lack of uniques that would fit any particular run due to RNG cruelty, but melee lovers were left in the dust apparently. I think there should be atleast one melee exotic to make up for this unfairness, maybe one of those suped up combat knives that were mentioned earlier.