I like the idea of Borgin or Burkes as RAB because the mind immediately goes to the Black family, however, I just can't get past the passing mention of a locket and ancient seals. What if these seals belonged to either Griffindor or Ravenclaw. in Order of the Phoenix. What is the significance of Harry owning this real estate if not to have possession of these items. I also posit this: What if Regelus is not dead? I mean how long was Pettigrew presumed dead but not. Would Kreacher have to listen to Harry if Regelus was still alive. Would that be magically known?