"Doubling total AD" is misleading. Being that it is AoE, this sort of item will mean that you take longer to take down individual targets, which is important for an AD carry. If you put out less single target damage, the enemy assassin/mage/carry might kill you before you kill them, resulting in a lost team fight.
Not saying at all that it is a bad item, especially if you are given time and room to fire away. But in terms of single target damage, its a decrease, and that is something that you can't overlook.
Why would you want 4 of these and a Bloodthirster when you can get IE and crit 3 people at once? But honestly, it can synergize well with certain champs...Ashe's Frostshot, Cait's passive, Teemo's and Twitch's poisons (Teemo will be even more annoying), Urgot's passive (your team won't be doing damage anymore), Graves' Quickdraw (because he needs buffs apparently)
What I don't understand is...why apply Blight stacks for Varus but not Silver Bolt stacks for Vayne? Sure, you have to activate the Blight stacks, but then you should just have it not apply either.
My Superheroes consist of the band members of the Who, Led Zeppelin, and The Beatles
Why would you want 4 of these and a Bloodthirster when you can get IE and crit 3 people at once?
Because the Hurricane's passive can't crit, as stated in both the linked thread and this one.
But honestly, it can synergize well with certain champs...Ashe's Frostshot
She already slows everybody with Volley, not sure this is a big deal.
Headshot every shot from bush. Funny, but probably not worth giving up real crits.
What I don't understand is...why apply Blight stacks for Varus but not Silver Bolt stacks for Vayne?
Because they would have to reprogram Silver Bolts to make it work. If you attack somebody other than the person who currently has rings, the first person's rings disappear. So if this applied Silver Bolts, it would end up making you never get the proc off.
And they want Silver Bolts to only mark one person at a time. It makes it harder to threaten people with the proc in lane and still get cs.