Outside of new shotguns, I think adding different bullet types you can switch between could make them a more versatile tool, just like in real life where in a blind, you can put in a single slug or buckshot in the barrel to deal with the situation at hand
870 vang comp: a modern 870 with either wood or polymer furniture and in use with police and FBI, could use the same animations as the 590 in game with some adjustments
KS-23: Russian 4 guage shotgun cause fuck your shoulder and fuck whatever you’re shooting at
Beretta 1301: a rival for the 1014, the different internals give it an edge in recoil control (for security)
Benelli M3: a pump action/semi shotgun, you could switch between different mods by pressing the fire select button
Kel-Tec KSG: dual tube pump action shotgun with a 14+1 round capacity (for security)
Vepr-12: AK shotgun with bolt catch/release
Genesis-12: an AR pattern shotgun (for security)
Origin-12: a fairly modern semi auto shotgun that’s different
AA-12: needs no introductions (highest tier shotgun given how powerful it can be and only found in area-12, not needed in PvP)
Also it would be pretty cool to have a super shorti (the Serbu) as a secondary alongside the pistols, short range and low tube capacity but handy in a pinch