I would love Valve so much to add this taunt, but I have a few things to mention:
The only part of the animation that was a bit clinky was the jump, everything else was perfect. It felt too sudden and his legs looked like they were on a set patha bit

Also, hitboxes? Ouch. Valve knows they gotta create a new hitbox where the pyro is on the balloonicorn AND when he's about to get on AND after he falls off. But if there's popular demand maybe this could be possible!

Just refine that jump a little more :D