I agree that this would be a really good idea. I usually carry a pretty large amount of weapons/firemodes (semi/auto, grenade launcher + different types of ammo for grenade launcher, frag grenades, red smoke, green smoke) so pressing the F key 5 times to cycle through my weapons has gotten me killed several times. I also once killed myself by thinking that I had my primary weapon selected, clicking, and getting blown up by my own frag grenade bouncing off a rock and landing at my feet.
Tl;dr. Very good idea, please implement it BIS!