It's hard to say since he's two and he definitely has not stopped growing. I'd imagin that his front will grow more, making it more even with the hind-quarters....taking off the appearance of being almost swayed back.
Once he is fully grown I think he'll be quite the reiner in the show ring.
How old is he? He looks a bit long in the back and very downhill. Depending on his age I would say sway back but it all depends on whether or not he might be really bum high from a growth spurt.
As I previously stated, he is a Hollywood Dun It grandson and he just turned 2 years old....and I think his back is rather short...I think he is going through a growth spurt because he had a really nice straight back a few months ago.