Okay get ready for this, you don't do anything to shotguns at all. Shocking I know. The issue is all but 2 maps off the top of my head are close quarters maps, and even those two are still medium sized. If larger maps with very open areas were made then people would be inclined to use other weapons. I enjoy scout rifles and snipers in vanguard activities but they are useless in the crucible, it's all about close range shotguning and high rates of fire. Bigger maps are a natural solution to the problem without nerfing for a third time