Item or Chamion ability that does extra damage to shields.

shields are rare/weak enough that they dont need much counterplay, especially since they usually have very small active durations. Closest thing i can think of as a "shield buster" is Vi's Denting Blows.

Work? Yes.

Make any god damned sense or be even remotely necessary? Not in the slightest. Shields are like heals that you don't have to get rid of, because they generally get rid of themselves. If you think shields lack counterplay, you need to stop facerolling, wait for the shield's duration to pass, then reengage.