It'd be interesting to have a non-unique melee weapon that uses ammunition, like the Ripper or a shotgun glove or something. It'd add a bit more variety to melee characters for certain.
Things like an electric powered chainblade are feasible. The "Doomishness" of such a thing is debatable. But on the other hand, if a chainsaw has enough petrol in the tank to run it for the 20ish levels you'll have it, then why wouldn't a single 9V battery work in a chainblade?
Combining the two possibilities, though: Chainsaw Mods! If an AoB clears the Chained Court, then ~5 levels later you come along a new red staircase, which will contain 1-2 chainsaw mods, which require ammunition as their raw power.
Possibilities include:
Electric Turbo Motor - increased chain speed! (weapon damage, requires cells)
Gunpowder Extractor - carefully timed explosions! (weapon speed, requires bullets)
Shotgun Booster - harness the knockback power! (movement speed, requires shells)
Depending on how you want to work "balance", either you could only use one mod EVER, or you can apply two mods, but only have one supply of ammo loaded. The chainsaw then has a clip (of varying size, perhaps clip size mods can then be applied with Whiz Kid?) which one loaded will be depleted with use. In the case of speed or damage, every attack (even if it's a miss) will use up ammo. And in the case of movement speed, every move will use up ammo. Perhaps every second move if you're running.
Thoughts?