I've been thinking about this a lot, as well. The first response always feels like, "Well, let's nerf shields," but that doesn't solve the underlying problem. There aren't enough actual counterplay elements to shields other than pure damage, but most shield-based champions have solid disruption tools (Lulu polymorph/slow, Karma slow/root, Orianna shockwave, Janna being Janna) on top of the number of support items that offer shields, as well.
Why not offer itemization options? A shield-breaker item would be a very interesting way to offer meaningful counterplay to a heavily defensive team comp that you would need to opt into, as opposed to simply toning down shield power and shifting the entire meta all over again. You could even make it multi-capable by designing it as a potentially hybrid item:
Spirit Crusher
Haunting Guise + Serrated Dirk + combine cost = 3000-3200 gold
250 health
25 Attack Damage
25 Ability Power
+10 Lethality
Passive: Unique - Eyes of Pain: +15 Magic Penetration
Active: Unique - Shieldbreak: For the next 6 seconds, you deal 10% bonus true damage against shielded champions that bypasses all shields.
It might just be an idea, but I feel like there needs to be some sort of itemization to counter the huge shield meta happening right now, because honestly, nerfing shields just make something else huge and OP.