No, this is a stupid idea. Grievous Wounds was a bad idea and the game is worse for it. It never put a dent in the lane dominance of Soraka, Alistar, Sona, and Taric back in the day so those champions needed to be reworked. There was no benefit to having a counter. All it did was make Swain and Mundo binary as fuck.
Similarly, now Lulu and Janna are top tier, and guess what? This wouldn't change. They'd still be able to stop aggression in lane because people have to farm before they can buy the counter item.
And just like with Mundo and Swain, a generalized counter to shields would impact a lot of shields which are balanced and healthy like Hexdrinker/Maw, Sterak's, and pretty much any champion with a personal shield.
The problem is specifically Lulu and Janna. They are so good at just stopping damage that they barely ever need to take risks to be effective, unlike most other supports or champions in general.
When something is OP it needs to be nerfed. It is really stupid to add a generalized counter which shits on everything that's balanced in an attempt to balance the few OP outliers. This is proven by history.