I would welcome that for example switching to grenade launcher and back to previous weapon will be possible with just one key (Q).
For me, when I played Nader for first time, it was really uncomfortable to use key (1) to switch back to SMG.
My suggestion:
Q → Grenade Launcher
LMB → shots fired (I mean nades)
Q again → back to previous weapon
(bind keys may vary ofc)
or just bind your keys/buttons differently.
for example, for my Fletcher E is exploding sticky-bombs and Q is throwing them I think.
Sorry, but pressing Q 2x for switching TO and BACK from a weapon, would mess up the system for other characters, I believe (like for Fletcher, for example)
But as the saying implies: “Man is a creature of habit”. You will get used to pressing 1-4 or using the mousewheel 
I will, I will. It just felt weird, maybe too much CSGO recently and I didn’t use mousewheel for switching weapons since Call of Duty 1.