excuse me, but doesnt jayce have the same problem as lane alistar used to have?
remember when alistar was changed to automatically execute an auto attack after his headbutt? people used that by running sheen on him and repeatedly trading with their opponents by headbutting them away in lane, dealing significant damage every time that couldnt be dodged or avoided, while making it impossible to trade back.
alistar was quickly nerfed because of this interaction.
now my question is, how does that differ from jayce repeatedly trading with his q + max health damage knockback nuke in hammer form? shouldnt something be done about this ability before he receives any buffs?
just. make it somehow conditional so its possible to play around that instead of getting point and click nuked with a gapcloser + knockback.
you could give him the nidalee treatment and have him require to hit you with his q in cannon form before he can get the knockback on his e in hammer form on you (he can still have the damage either way, just not the knockback).
this would also give him a window of weakness to get engaged on in cannon form when he misses his poke. he doesnt get a 100% reliable disengage.