What? Eccleston's had Ten-nish hair before. See? Well, sorta. But anyway, instead of, erm, NineII been sent off with Rose to the alternate universe, Ten, Rose and NineII "enjoy" each other's company aboard the TARDIS. Or, he can still have the close-cropped hair. That works too.
Yeah, just surprised this hasn't popped up anywhere since the hand regenerating into Nine is already out there.