what isn't there an aoe qss

because it would be broken

Because having a support buy it for literally the whole team is just ridiculous. They already have to load up their inventory with actives. I think Malzahar, Zed, Lissandra, Brand, and anyone else who gives a debuff would be useless with an item like that because rather than "Kill the guy without the QSS," it's "Don't kill anything for the rest of the game." It would particularly make assassins complete garbage in general because most of them apply some sort of debuff to deal damage. (LeBlanc's Q, Zed's R, Diana's Q [not technically an assassin])

I highly doubt it'll happen.