I agree, it's an accessory that is badly needed, to make rear lights easy to mount in a place where they can be seen.

The PBSF mount is almost a good idea, except that it necessitates removal of the reflector, which is a requirement in many jurisdictions.

It would be nice to leave the reflector, center rear, and mount other lights on either side,(on the sides of the rack-rear of the panniers) with an option to have the actual light more toward the rear, or up.