I just wonder if anyone will ever solve the pendant mystery(assuming there is one).
I would not be surprised if the pendant is just for trade. There are some areas that are pretty weird, like they seem to have some sort of purpose but there's absolutely nothing that can give you a clue or something.
People have tried a ton of stuff with Solaire since the description in rings, items, miracles and his weapon and armor say that he is more important that what he actually appears to be since he was some kind of Deity or Demigod many many years ago and that's maybe one of the reasons why he is searching for "his sun".
In any case I really hope someone in a interview ask about that because people has been going crazy with the pendant for a long time now.