For me, pool party vel'koz would be one of the coolest skins possible for him. Pool noodle arms, beach balls for eyes, a little floaty vest for his armor, and a watery interior for it to all float in, in place of his glow. I don't see it happening but there's hope. After all, rek'sai got the jetski skin!
What's your skin that you really wish would be made, but you're just stuck being hopeful on?