@Riot - Bonus dmg vs shields is a mistake
Irelia's passive gives her bonus dmg vs shields when she's at max stacks. I think this sets a bad precedent and is a mistake.
Shields as a mechanic have the best clarity possible. You see visually how much the shield is worth relative to the champ's health pool. This is only true when damage has the same effect on the shield as it does on health. With Irelia's new passive this is somewhat less true. The clarity is muddied.
There are shields that have been OP or caused issues. I think the problem is when you can have a high impact simply by shielding allied champs, because this is not interactive with opponents. Janna, Lulu, and Locket tanks have had this issue recently.
And I don't think providing counters to shields fixes the issue. If the champion or item has impact in an unninteractive way you're not fixing that by providing a way to cut through the shield. All you're doing is reducing their impact, so you might as well just nerf them instead of putting in a counter. The counter also effectively nerfs and muddies the clarity of healthy shields like Sterak's or pretty much any personal shield any champion has.
I think the better option is simply nerf shields that have uninteractive impact and move power on those champs/items to healthier places.