Devs have made it relatively clear that they're not in the semi-auto shotgun boat, as they think it will be unbalanced, even though it could be argued against that fairly easily or even balanced accordingly to suit it to the game without infringing on the innate concept of the shotguns themselves functioning as they should.
I'll be listing a few things that came to mind in terms of balance below, but if you have any ideas feel free to add them!
- Recoil, yes this one is pretty obvious
- Supply point cost
- Ammo-type restriction
- removing ability to have laser sight
- Only having long variants with long stocks on them giving them the same issues as using other longer weapons in tight confined spaces
- mode-restrict it, have it only for coop, or just exclude it from competitive
- add serbu super-shorty shotgun to Breacher class as secondary option for 4 supply points, you'd be limited to 2+1 with it so it sort of balances itself out