I think an item similar to spear of shojin where it procs under certain conditions or you need to activate it to cut shielding in half. The shield power and excessive healing is still problematic in my opinion, some champions just feel unkillable even with grevious wounds applied (thornmail, executioners).
Would appreciate some feedback on this with any more refined ideas or criticism.
EDIT: (This is copy and pasted from one of my responses below, to help clarify the idea)
Spear of shojin has been used as an example because it's a situational item on alot of champions that can utilize it (excluding renekton, riven I guess). The point of the item wouldn't be to just destroy the entire shield, but to reduce shielding on the target. It's stats can be done so that it becomes VERY situational, it WILL have better options for champions to take over the item where there is only a support or a champion that self casts shields on themselves or the ally. The entire purpose of the item would be to be taken for the situation and not for it to be mainstreamed into champions build paths and kits.
There's grevious wounds that can be used to reduce life steal, but it can be normalized if the champion that utilizes gw it doesn't stack full armor and the attacker builds more life steal or can still sustain through it. I'm no expert on the thornmail, but in my humble opinion I believe bramble vest has slight better cost efficiency over the thornmail (which I rarely see people rush/build right away after getting bramble vest (this excludes rammus)) and in my belief the item should only apply grevious wounds and not deal extra damage on top.
It would be similar mechanic to shield power, if you build enough shield power it would battle through the shield reduction.
And to clarify, this isn't just to target the support/enchanters. This is supposed to help with working around excessive shielding in certain champions, either shredding the shield with some multiplication/percentage to having to be applied in a similar way to grevious wounds where the current shield is intact. I would imagine this being good against the Sona/Taric strat in a way, where it doesn't really seem to be that played, it would still be a decent pick to somewhat counter that unstoppable duo.