I had a few ideas regarding Aatrox. Whenever his Bloodwell is full, he gains additional effects on his abilities.
Q, costing 10% CURRENT HP, could give him a shield for 10% MAX HP. Kinda like how Zac's blobs heal him for MAX HP when they cost CURRENT HP.
W could give him a movement speed buff every time he procs either Bloodthirst or Bloodprice
I would rework his E to be an auto-attack enhancer/reset that slows the target and sends out the blades behind the target to deal the magic damage and slow.
The bonus effect on his E would be a reduced cooldown every auto-attack.
I would rework his R to deal the magic damage, but also give out an aura to nearby allies that increases the amount of healing they receive from all sources by 10/20/30%
Of course, the damage on his Q, E, and Ultimate would be reduced to compensate, but I think it could make him a much better champion while keeping a lot of his identity and gameplay in check.
Also, they need to increase the time it takes for his Bloodwell to start decaying. I can't even go ward my lane without it starting to drain.