Well let's actually consider what OP is saying. Speaking from the mindset of what I assume is a skilled Yasuo player, (I refuse to pick him up because O've got a little dignity and I'm also bad) his wall will be used reactively instead proactively. Considering balance changes are made at high plat/up, it's easier to assume he will block most skill shots that aren't beams or damage adjacent areas to a champion (IE Annie's W. Mordekaiser's E, Lux's R, Taric E).
A good Yasuo player will only engage on a fight if the following are true:
-There is little hard CC available to keep him out of position
-He is too fed to care
-His 2 crit items are done
His primary role is that of an assassin, and he gets away with a lot because of dual passives (which is another balance idea I heavily question)
His Wind Wall provides a stationary Braum Unbreakable with the only drawback of the ability is that is has a fairly high cooldown, and can be moved around. It allows allies to fire projectiles through it, while stopping enemy projectiles.
It's strengths are clearly defined and readily apparent, and has better defensive capability than that of a tank role.
I believe that Yasuo's windwall should block ALL projectiles, not just hostile ones. This would create an inherent risk for both your team and your opponents, forcing everyone to play around it, much like Anivia's wall or Trundle's Pillar (minus the slow for allies).
This balance suggestion I understand would likely cripple most Yasuo players, and the people who benefit from the exclusive efforts of a skilled one. But considering that there are other abilities in the game that can harm just as easily as help, I believe this would remove some of the irritation many players have to go through when battling against a Yasuo who is winning a game 1v9.
TL:DR
Make Wind Wall destroy all projectiles, not just hostile ones.