In truth, the various shells have significantly different tactical applications, so trying to streamline them into one system would be disadvantageous in my opinion. A scoped shotgun is obviously appropriate for slugged ammo, but the scope becomes superfluous for CS or FRAG-12 applications. Equally, a tactically equipped smoothbore is inappropriate for a slugged round.
Swapping out barrels & sighting blocks is the obvious choice for one platform. Not that hard, but one wouldn't take both into the field, unless you had a dual barrelled weapon perhaps.
Realistically, a slug round isn't that advantageous over other conventional weapons. It'll hit hard, true enough, but with limited range, how is it any better than an M4 or other AR?
Regards,
John