Assuming Quinn's changes were intentional and not an accidental roll-back to a previous testing version (like I imagine Tristana's Rocket Jump changes were?) - you're testing having Quinn's Blinding Assault reduce the enemy hit's sight radius and remove allied vision? Seeing the video on Surrender at 20 were Sivir is forced to walk slightly closer to hit you - it looks awesome!
Is it affected by tenacity? If no, why not?
Thinking about Sight Reduction as a crowd control effect makes me wonder, though, why not have **all blinds** works this way? Well, actually, there's only Teemo left with Blind now that Quinn's gone... why not make Teemo work this way? This could afford the little devil a little more power in his budget since he wouldn't be so obnoxious versus melee any more. Sight Reduction and Blind should be the same thing; the cannot-see crowd control effect (along side cannot-move, cannot-attack and cannot-cast).
tl:dr; Why not make all "Blinds" reduce the target's sight radius INSTEAD of giving them 100% miss chance.
1. Graves' Smokescreen would now _called_ a persistent AOE Blind.
2. Nocturne's Paranoia would now _called_ a global Blind. As Quinn's should be, Blinding Assault and Paranoia are now affected by Tenacity.
3. Teemo's Blinding Dart _could_ be reworked similar to Venom Cask - Blinding Sachel, hurls a pouch of dust that does AOE damage and Blinds multiple targets. This is to compensate Blind being weaker versus melee opponents. It could easily remain single target too - I'd hate to lose Omega Squad's knife to the eye, but I guess a well animated flashbang would be cool too. (Maybe the knife as his crit animation? :D)
4. Taunts, Charms and Fears _could_ apply Blind, making it so the source of your problems is all you can see. Malzahar's ultimate, too, since he's locked eyes with you and is pouring the void into your soul. Likewise, Amumu's ultimate could Blind instead of Disarm (i.e. Entangle = Root+Blind now), since he wants to be attacked for his Tantrum passive and the notion of wanting people to pay attention to him suits him thematically. You could even add a screen overlay of bandages covering the camera, to make it look like Amumu is turning you into a sad mummy too. Sight reduction on powerful effects like this would also help you see that you're under someone else's control. (Similar to Tahm Kench.)
6. Kha'Zix's Taste Their Fear's binary "it's either too wide for Kha'Zix to use or too small for enemies to relate to" _could_ be reworked to interact with sight radius - affected by line-of-sight (terrain; if you and your ally are close enough to hold hands but still separated by a wall - sucks to be you!) as well as sight reductions. Kha'Zix would be the king of the jungle but relatively weak in open areas. To make him not entirely reliant on his ally's CC or his enemy's being out of position (although that is suppose to be what an assassin/him in particular is good at) - Kha'Zix's Void Spike could apply Blind.
Although, minions and monsters in all cases should probably still just have 100% miss chance - 'cause sight loss doesn't really affect AI... EDIT: Which you've just done on Quinn today. Well, you used Disarm versus non-champions but still. ^_^
Another pro to this change: you no longer have the visual feedback of blind being "miss". I CAN SEE MY ATTACKS ARE STILL HITTING YOU- WHAT SORCERY IS THIS?
tl:dr2: Blind now reduces the sight radius of champions to X and removes their allied vision; versus minions and monsters they have 100% miss chance on their attacks. Existing "sight reduction" effects are now called blinds and are affected by tenacity.