I think before we comdemn Vayne to the nerf bats, BORK should be looked at first.
Look, I get it, Vayne's currently the most popular champion right now. And yes, despite her supposedly having a weak early game and having a moderately high skill floor, she's at a much higher win rate than she should. However, I think that the issue here is BORK, not just Vayne.
BORK has been unbalanced for a long time. It's just the tank meta and the meta favoring burst AD casters over hypercarries kept the item from being looked at. Riot may have nerfed the active portion of it, but the passive portion's scaling is what's really breaking the item right now, especially its broken synergy with sated devourer.
Because I get the feeling somehow that if Vayne is just dumpstered without looking at BORK, you're going to see a lot more "protect the Kog'Maw" team compositions. Oh, and Kog'Maw, I shoulda mentioned that too. Lucian will probably make a comeback too.
Teal Deer, I think Vayne's biggest problem is how stupidly OP BORK is at the moment. Just nerfing Vayne to sate the boards' bloodlust is just going to have her replaced with another hypercarry or two.
then just having a last whisper isn't going to help you melt through their 4k+ health, you need the 8% current health damage of 
is ridiculous in terms of lifesteal and makes duelling champions like
absolutely ridiculous because no matter what you are doing you are stealing Obscene amounts of health.
, which is no longer just 'Hey, more Spellvamp, AP and CDR' but is now more focused around Duelling Tanks who have MR to counter base Spellvamp values.