As they've gone down again I thought I'd give a shot at some changes xD
I think Ahri is actually in a decent state now that luden's fixes mana and adds a bit of damage into her kit. That being said, she lacks a way to create pressure. She pushes waves okay, but not enough to get a pushing advantage vs control matchups. She can kill opponents, but she doesn't quite have enough damage to create kill pressure. Most of what she has is roam pressure, but it's hard to do that if there's a jungle gap. She also doesn't do a lot of damage to turrets, so it's hard to threaten towers. Her ability rotations are also not enough to chew through tanks in the later stages of the game. There is also adding more utility into her kit, but I think her mobility coupled with her charm is enough.
So how to fix this? Something needs to be added into her kit to create some sort of pressure, so that she can force her opponents to do something instead of waiting for them to make a mistake. Her wave clear is already decent enough, and added that she has such high ability to roam, I don't think it's a good idea to increase her pushing power. For kill pressure the dfg charm would do okay, but the changes to the w completely countered the extra damage, in addition to making her engage patterns very predictable (it also made her clunky...). The current movement speed on her q adds to her roam pressure without, in my opinion, making her overbearing (I know people find it frustrating though).
This leaves turret pressure as the last variable to mess with. It would be nice to have a way to empower auto attacks, and maybe give it's range a little boost (her auto range is already decent though so that might be a bit much). This effect could be added onto her w, and the empower could either be a lich bane effect, or a damage over time effect that works on both champions and towers. This effect would also give her a way to whittle opponents down over time, and eventually threaten an all in, but still gives the opponent priority to decline if they feel they are too low. The burning effect would also fit thematically with the foxfires; one idea is to have her next auto be a thrown foxfire to indicate that it's empowered.
TL;DR: All Ahri needs is a way to create pressure. Adding an effect to her w that causes her next auto attack to either have a lich bane effect or a burn effect that works on turrets and champions would be the best way to accomplish this. It also fits thematically if her next auto is a thrown fire orb. This change would also allow her to whittle down enemies health, and give her kill pressure while still allowing enemies to react.
I'm curious to see what everyone else thinks on this.