If you really want to buff Jayce, i have a suggestion for a small buff
Change his W autoattack damage from 70/78/86/94/102/110 % to 70/80/90/100/110/120 % - also for the sake of clean numbers, the 8 % extra is just ugly to look at. The original reason why it was nerfed was Crit Jayce being too unfair, but that build is subotimal now, with only Essence Reaver and IE are good items for him.