I've been maining Ahri since season 3, a lot of people who never played with old assassin ahri probably won't agree at first, but let me explain. Ahri needs that .6s delay to counter the animation lockout between her w cast and charm.
Why is this important? To deal damage with your W consistently, you need to be in your opponents face, if you cast your charm from a distance, and then w in, there is a chance you're w will spread out, so you want to be right on top of your target to get the most damage off. Unfortunately, if you get in too close and charm first then W, you've prolonged your time of danger and still won't guarantee the damage, however, with a .6 second delay on w, you can get next to your opponent, W and immediately charm. Both will land nearly simultaneously, but charm will land first and you'll get the full damage amp effect as well. This will also maintain the consistency of ahri's W>E>Q combo at close range and keep her [W>E>R>Q combo](https://www.youtube.com/watch?v=wc-4R6Sf0PE) for all ins.
Essentially, what i'm trying to say is that if there's going to be a delay on W, it should at least be long enough of a delay so that it works in cohesion with the animation lockout that occurs between her W cast and E cast time. This will promote the higher skill floor that seems to be sought after.
Edit: to clarify, today's changes have listed a .5 second lockout for w agro, W>E makes the w hit first. However, on the first iteration, the W had a .6 second Lockout and allowed for the interaction i desire.