Wall mount TT shelf is NOT an excellent idea. The house's wall in North America are usually made of dry wall. If a TT shelf mount to the dry wall in the Hi-Fi room., the dry wall(large surface area) will act as a giant DIAGHPARM and will transit the vibration(causing by sound wave) back to your TT.
Unless the wall are solid concrete then it might not be a problem.
Unless the wall are solid concrete then it might not be a problem.