Not sure I'm with this idea. It's not that I don't think a Dragonslayer Yasuo skin would look good, but thematically I don't know that it fits. Jarvan, Braum, Vayne and Pantheon are all rough-and-tumble sorts. They're....brawlers. Yeah, they're trained fighters (well maybe not Braum), but all of them, are about moving in on you and powering through to victory. Pantheon, Braum and Jarvan live in the middle of the enemy team, and even Vayne gets into the middle of things and mixes it up closer than any other ADC except Graves. In contrast, Yasuo is an elegant swordman who moves in and out of combat and sets up combos to work off of. He goes all-in, sure, but only when he has the advantage via knockup, whereas the four live Dragonslayers are more like see opportunity, cause bodily harm to opportunity, if that makes sense.
Assuming we wanted a midlaner to get a Dragonslayer skin, my money would be on Diana. She fits the same kind of "I'M GOING IN" dynamic that the other Dragonslayer champions have going on.