I agree with everything except for the part with the shotgun buffs. Imo you'd just end up having tons of corner campers using the spas and one shotting you instantly. Especially in combination with the perk to get a second primary this would be even more obnoxious, because they could literally take a sniper rifle and shotgun combination and f*ck you over at every distance (even if snipers got nerfed). I think the mechanic that you need to headshot with shotguns to get a (slightly more) reliable chance to oneshot people is a good thing, because it adds a level of skill to successfully corner camping and oneshotting people (since you need to hit them in the head to oneshot).
I like experimenting with the different lethals and I noticed a strange interaction with the remote bomb and the skill "magazine pouch". If you take this combination, you will (obviously) end up with two remote bombs. But sadly, you can only lay down one remote bomb at a time! You have to detonate this one first before being able to lay down the second one. That's where my suggestion comes into play.
I'd suggest to make the button for the remote bomb solely for laying them down, and to make a seperate hotkey for detonating them (perhaps even two seperate hotkeys, one for rb1 and one for rb2). It might be best to make this optional though, because I've seen some people using the remote bomb to throw it over walls and detonate it instantly, which would be a little more clunky to do if you had two different buttons for that.
Imo the remote bomb can be a very competitive tool because it can be placed at strategic angles so that it's hard to spot, and also because it's detonated manually instead of automatically. I've had a couple of double/triple kills with it by placing it somewhere around A/B when defending in S&D and detonating it at just the right time. Implementing my suggestion would allow for more skill expression with this lethal weapon as you could have two of them active at the same time and detonate either of them at will.