Has anyone mentioned tighter spread? Tight spread, and by extension accuracy over range, is the one niche that has yet to be filled by the shotgun load out. If one could snipe head shots with the m4 as if using a slug, it would be uncontested in that regard. Imagine that, then consider the penetration that would carry over range as well.
I've also had that thought, but people tend to be non-plussed at the suggestion of a more-accurate shotgun for some strange reason, despite the fact that a weapon was introduced that filled that role in the first. Personally, tightening spread would be a wonderful buff for the M4, especially considering it looks longer barreled than the other shotguns.