Which conformation/movement 'faults' can you live with or improve with training and which are just beyond the ability of anyone to improve enough for the horse to be useable as a dressage mount?
For instance, I just considered a horse that has a slightly low-set neck. However, he hadn't been doing much work so wasn't muscled over the topline. He also was very well balanced and uphill when he moved in all three gaits. My thinking (wishful perhaps?) was that the neck could be improved with work and wasn't holding him back from moving uphill. (He also had strong hind quarters and a wonderful temperament).
Anyone want to give their opinion and experiences on this topic?