After dealing/playing excessive ekko games I have to say
R needs huge mana cost for what it does, its a pretty huge game changer when used correctly you can decide a skirmish/5v5 quite fast.
Mana costs on abilities in general need to be higher.
Decrease scaling of E and base damage Decrease scaling of W and base shield.
His Q is fine Imo, solid spell could use better scaling though imo. The immediate through damage should be moved slightly to return damage Not sure why it stays after he dies though, other champions don't get that mechanics (talon for example loses W/R on death)
These nerfs are ideas, not do all at the same time.
I don't encourage gutting but he needs nerfs and these are simply starting places. He's very redic right now and he needs nerfs. But what exactly NEEDS a nerf is up to dicussion.