Ahri gets the Blitz treatment
If Q doesn't hit an enemy, Ahri is briefly slowed upon return. This fits thematically because she failed to take souls for herself, and it forces her to think instead of just randomly throwing Q for a speed boost whenever she wants one. The slow could be masked with a cast of R, creating a gameplay pattern.
What this would do is make Ahri want to poke through minions in lane, so if her enemy baits her into Qing without minions, then dodges, she will be slowed and can be engaged on/hit with skillshots. Outside of lane this forces her to aim carefully and creates a window to outplay her (or for her to outplay an outplay, ad infinitum).
Idk where she sits in terms of power so mana cost buffs or something to compensate maybe, I just like the idea of this mechanic.