Not a horse I would buy just from this picture. Might not be the most flattering, I don't know. Don't like his neck and withers. Might even be a little too ribby even for a TB.
Generally I'm not a big fan of the overall look. I like flashy horses with a lot of personality in their face. I'm sure he's lovely but since I know you are looking to buy those would be my thoughts if I was interested in buying him.
Yes, an ewe neck will make muscling and collection harder. A neck that has the proper "curvature", for lack of a better work, will put a horse in a natural, easier to work with, frame.
His back is quite long. This also makes collection difficult. He's underweight and not well muscled (that can be changed, with good feed and proper work). I'm not a huge fan of his long gaskins, but I'm no expert with the hind. He looks to me a little camped out in the hind, but it could be the picture. It looks like he has a pig eye? Again, could be the picture. Nice front pasterns! Theres a nice line going through his withers down the center of his front leg, that's good.
The main thing that I worry about is that long back. It creates a lot of problems, from collection issues to, most importantly and commonly seen, back issues. A long back is a weak back.