Hard to tell (for me) which will continue to grow their spikes in, but if that is what i'm selecting for, i don't think that it will be a problem with this line. I'll try to keep track of percentage, tho, as time goes on.
As far as the hens having U shape backs, it will take some more maturation. The birds are all over the place with molt and growth, at this point. Bare backs in pictures, or otherwise, makes me cringe, and i really hate to post photos until that gets worked through.
Totally understood -- The dinosaur stage and adult feathers replacing juvenile feathers is always a wait-and-see with chickens. Some people really concentrate on the feathering but I personally like seeing type correct first -- U shape back and spiked rosecombs -- and of course, a sweet outgoing curious friendly temperament as most Doms are known for!