Some post.

I feel that Jinx's W is fine as it is, currently. It's a strong nuke early game, but drops off a bit around  midgame/lategame (as it should) because you have to stop to cast it, which leaves you vulnerable to harassment or just getting dove on (since unlike Caitlyn, you do not have a reliable disengage) and the damage and slow stop mattering after a bit. Not to mention it's extremely telegraphed (roughly the same speed as Caitlyn's windup on her Q, while also having an path showing exactly where it goes).

Even with the low cooldown on W when it's maxed, you won't really be casting it when hard committing to a teamfight, since your job as an ADC is to do as much DPS from a safe position as possible, and any time spent casting W or R is precious seconds of damage you're missing out on. You will notice that this is basically why Caitlyn autoattacks 95% of the time when hard committing to teamfights (in fact, Jinx and Caitlyn share traits as ability-based lane bullies that transition to autoattack DPS in the mid/lategame due to spells taking too long to cast without losing DPS from doing so). At most, you'll be using it to poke in the pre-teamfight phase (players are dancing around each other trying to look for opportunities to initiate and thus hard commit to teamfights) and in the post-teamfight phase (all major cooldowns are blown and one team has come out on top with a numbers advantage).

On paper, it does tons of damage (with 300 AD, max rank W does 210+420=630 damage per cast), but by the time you get to a point where that matters, which basically means you have all your core items, the enemies will have armor, and even if you factor in penetration from LW and masteries (for argument, let's pretend we're casting W on a target with 200 armor), your poke won't be very potent to start with.
When casting on a 200 armor target with LW+ArPen masteries, you will reduce 200 armor by 115 (200-80-5), which comes out to roughly 54% damage reduction. This means that your poke translates to 290 total damage (real number is 289.8). Meanwhile, an AP Nidalee with around 500 AP will do 575+812.5=1388 (actually 1387.5) damage with spears in her best case scenario, which happens more often than you would think because her spears are harder to react to due to not being telegraphed. This is of course reduced by MR, but you most likely will not have 200 MR and even if you did, the numbers would come out looking roughly the same as the raw damage on Jinx W.

Plus, it's already been nerfed on PBE if I'm not wrong---it costs slightly more mana and does less base damage early on while retaining its lategame damage. It doesn't need more nerfs.