This is not the buff that Yasuo needs. He is already incredibly toxic. More mobility is not the answer.
The biggest problem with Yasuo is that he's actually a very generic champion, with the most simple of abilities. The problem is his E and passive are like simple abilities buffed through the roof. Because of this, the only way to make him not toxic is nerf his damage and give him more survivability, but that would make him a boring, generic bruiser, except sacrificing any real cc for mobility.
Think about it. This ONLY benefits him when he's getting kills, and not helping at all when he's not. Look at other champions with mechanics like this. They're feast or famine. Kha'Zix and Katarina are worthless when behind, and broken when ahead. I don't want him getting buffs for when he's ahead. I want him getting buffs for when he's behind, with slight nerfs to his late game potential to balance it out.