Good idea? Bad idea?

Depends if they have any on-hit effects that are triggered by Runnan's bonus projectiles, and whether or not inflicting those effects on more than one targets is better than having another item that increases your damage against a single target.

Hurricane + statikk shiv = awesome aoe
Those two just do so well together, I'm not sure if you should just get one or the other.

SS is good, but PD out-dpses it even versus more than 1 target.

It benefits some champions more than others. I prefer the Shiv over it as Ashe (for the crit chance) but I get Runaan's on Vayne to get true damage more often.

Can someone please explain to me a situation (or an ADC) where you would build hurricane?

I have been trying it on vayne because I had the same train of thought, but my team always rages at me when I get it.

can't tell you if its good or bad having never done it myself but ive never seen it. at the risk of sounding like a sheep, if it was a viable build then i assume that it would be used here and there.

you buy warmogs on everything and you win

Depends on what you're up against.
If you need fast clear times for farming and find yourself capable of positioning well enough to make use of it in enough big team fights, then grab it.
If your team is primarily engaging in smaller skirmishes, or your team is already able to push lanes fast when needed and now needs you to take down structures ASAP, your gold may be better invested in other items.

I really don't like the idea of anyone getting it on vayne..