I agree that the Riot Shields need a slight nerf because of the ability to not be exposed when tossing explosives but other than that, the perks will not be nerfed and nor should they be. Whenever my buddies and I run into a team of Riot Shield users just use the following:
Assault Rifle: Grenade Launcher attachement
Perks: Danger Close, Off the Grid, Recon, Sleight of Hand
If more than one person on your team uses this, you can decimate Riot Shields. The Shield isnt strong enough to stop the noob tube and its a pretty easy double/triple kill when they all group together. Or if you want to really piss them off just use a Riot Shield class with Radar.. Off the Grid. Reflex. 2 Lethal, and Akimbo P226 + Throwing Knives.
Just wait for them to walk right by, then pop em in the back with a knife cuz they couldnt ping you on radar.
When ppl come at you with a team of R/S, don't get frustrated just get creative.