I really don't feel like Ivern needs a nerf. :/ he's got a high winrate but his pick rate is low; that's like saying Kog'maw needs a nerf because he had the highest win rate for ADC for a while(IE Before Lucian got super OP and popular). He didn't get one because his pickrate was low; it was literally just a pocket of players who were good at him playing him and bloating his winrate. I feel like its the same for Ivern.
I also don't feel like Ahri needs a nerf either. She has literally had nothing change to her specifically that makes her win rate high; its just high because of the result of the meta. Immobile mages are not really able to go mid with the mobile AD Assassins that have become super popular as of late so its understandable that people would settle on something that was more mobile if they needed AP for the team. And Ahri fits that bill.
Lucian definitely needs something. He has recently been buffed and changed and I think it was an over buff when they were already were changing BoRK. He is WAY too strong now with a MASSIVE play rate. He's always, consistently been a favorite ADC to play by a lot of people and when he's good, he's too good. :/ He's so oppressive and stifling.