My main concern with him would be saddle fit. I would think he would be hard to fit a saddle to because it would always be sloping downhill onto his shoulders. And that's not only uncomfortable for the horse but the rider will also feel like they are going downhill as well.
Even though I wouldn't label him as roach backed, he really has the overall "look" of being roach backed because there is such a pronounced dip there. That's the first thing that jumps out at me looking at him.
Other than that, I think he's beautiful! And I mean that sincerely. He's a really attractive horse other than the shape of his back. And that's mainly because I wouldn't want to ride him for fear I would always be riding downhill. I know his withers are fairly level with his croup. But that's not where the bars of the saddle are going to fit. But hey, I just trail ride, so take that with a grain of salt.