Jayce Nerf Alternative
So let's talk about 
(Skip to the 4th body of text underneath this text if you wish to skip to the main stuff)
As you know, Jayce was recently nerfed somewhat heavily in patch 5.1 as can be seen on the patch notes. The purpose of this is to present an alternate way to nerf Jayce while also promoting more use of his under used Hammer Stance.
Let's start first off by addressing the reasons that Jayce was nerfed. Riot justified the nerf, by stating the following, "For a guy so strong when it comes to long-range combat, it doesn't make the most sense that he should blow you up in close-quarters without the use of his hammer."
I agree with this, his damage was insane considering that it was over range, and, if you got up close to him, he would just simply activate his w and 3 shot you if he was building full damage. Essentially, he was dealing Talon-like burst damage over range, something that didn't require him to put himself into combat, or putting himself at a disadvantage by locking himself in his melee stance. That was simply too strong, and too safe for the damage that it did. As a result, he was nerfed, his w had its damage reduced significantly, from 130%, to only 110%. This was quite a huge nerf considering that he relies on this ability for the majority of his damage come late game. However, I have an alternate way to deal with his damage, while still granting him his heavy damage, just with far more restriction, and risk.
My preferred nerf route is to have the damage from his W max out at 110% in Cannon Stance, and max out at 120% in Hammer Stance. So, what would this mean for Jayce? It means he still loses his ability to deal the damage that he did before over range, something not very many champions can claim to be able to do. However, he can make the compromise to continue to do this heavy damage, so long as he switches to Hammer Stance and sacrifices his range. This would make it much harder for Jayce to deal his highest possible damage, because it would mean stepping out of his comfort zone, and engaging on his enemies in a way that leaves him extremely vulnerable and increases his chances of death by a huge margin. Instead of just sitting in the back pressing W.
So, on paper this would look something like this:
Active: Gains a burst of energy increasing Attack Speed to maximum for 3 attacks. These attacks deal 70/80/90/100/110% damage. These attacks will deal an additional 10% damage while Jayce is wielding the Mercury Hammer.
tl;dr:
Just because Jayce has the ability to deal powerful burst damage from a range without needing to switch to Hammer Stance to deal with enemies, doesn't mean his damage output should just be flat out reduced. Instead, his W damage should be reduced only in Cannon Stance, which is where the problem lies. Players should be rewarded with bonus damage for using Hammer Stance and putting a much higher risk on their assault. In addition, this would bring more use to Jayce's Hammer Stance, which as Riot said, essentially said, is highly disregarded.