You can actually use Mark defensively. Throwing it on a minion after you've been Marked can prevent a random flying Alistar from headbutting you into the rest of his team, or can help you negate any Singed fling, for example; Exhaust wouldn't do much, in those situations.
Sona/Heim/Ziggs have mantained the highest win ratios thanks to their kits; with a skillshot-like stun, or with Ziggs' W, all you have to do is timing them well while an enemy is dashing to your face, and you can get back to healing or poking (or both at the same time).
The problem is that this new spell didn't help who it was supposed to help - as in, tanks in general; it helped high close-range burst (Annie, Katarina) and aoe CC (Amumu, Galio), categories that didn't really need a chance to engage from the fog of war.
Since it's not perfectly calibrated either (you don't see the projectile in the exact moment it leaves a bush, or when it comes out from the fog of war; there's a slight area where it's not visible yet, although it supposedly should be. Also, the hitbox doesn't match the snowball size, it's bigger), and since it reveals stealth, even after you've been dashed to, it hurts generally champions who rely on range (ADCs like Miss Fortune, Ashe) and on stealth (Evelynn - wasn't she supposed to be helped too? - , Vayne - Tumbling won't save you from dashed champions cc, since it's instant, nor will Ult + Tumble, since you're still visible).
So, in my opinion, if this spell has to be implemented, it needs more work and thought. As it is right now, I vote no.