Was the Fiora VU necessary? I've started playing her quite a lot and I have to say her new gameplay is fantastic (don't nerf pls). One thing that bothers me though is that stupid walk that simply doesn't fit her at all. Any chance they could change it into something less... ridiculous?

Well, nothing is necessary, but I suppose that isn't a good answer.
Glad to hear you like her new gameplay. We had her kit in a finished state for a little bit, and wanted to find a time to ship it out. Since it had a bunch of visual changes that were needed to support the gameplay (basically a full VFX set and a need for animations), we went ahead and grouped in the model/rig/animation changes with it.
Fiora had her share of problems before, biggest one being that her silhouette was really weak, which was the largest push for updating her model. Her thematic identity was a little weak too, kinda just being... chick with sword. We didn't aim to destroy who she was, just increase the fidelity. We had an opportunity, and we took it. Hopefully you enjoy it on the whole.
Our aim with her animation set was to increase the dynamics and expressiveness as she's moving about- this is something you'll see in general if you compare older animations to newer ones. (This is a good link to check out on that: http://the12principles.tumblr.com/)
However, perhaps her run is just overdone. I can talk to her animator tomorrow and pass on your feedback.