Honestly? This would be a horrible idea. It's a good concept when you think about it, making tanks actually able to take the brunt of a blow, but now you have to think from a damage dealer's perspective. Almost all mids are purely burst. Pressing this item when they go to burst you would pretty much make you immune to their damage, functioning like a Zhonya's for tanks, but you're still able to move around. Mids already have issues with tanks since most are burst, not DPS, so a tank that can absorb their burst would essentially make them useless.
Then against an ADC... This would force the already horrible META to be all about escapes. It's bad enough that MF, Kog, Varus, Sivir, and Twitch are in a horrible place because they lack escapes. To then make their huuuuuuuge burst that they're known for nulled as well? Where does that leave them? It would make them completely useless until the enemy has used their item to negate the mid if they even have to.
There's also now the extra sticky tanks using this to dive in the middle of the team. A good form of peel is to burst the tank who just jumped in the middle of your team. Pretty good idea to do that so they can't destroy your carry. These champions are typically junglers though, but some have been known to go top, namely J4, Xin, and Mao. These three have the damage of the gods and the tankiness to match it. If they could now press a button and take a lot less damage? Well, instead of 3 or 4 tank items, they'd only need 3 to negate your team. Randuin's, Banshee's, and your new item. With that, they can get their last two items as their own big damage items to accentuate their already huge damage kits. Imagine a J4 with a Hydra and Scimitar diving into the middle of your team and locking your carry down, murdering it and it can't do ANYTHING because your team can't CC him because of the Scimitar, they can't kill him because of your item while he sustains off his Hydra, and they can't knock him away since he has two gap closers and a slow.
Don't even get me started on what that item can do with Cleanse. Scary stuff right there.
Also, I should likely mention the biggest thing. The only counterplay to tanks is Void Staff and Last Whisper. To counter an item that's a counter would be the same as making an item for Malzahar that counters QSS. It's just silly.