What about the thing of inherited will? Remember when Kaido knocked Luffy out of Onigashima, he expressed his disappointment at Luffy not becoming Joyboy. So, maybe there's something more to it, and it's indeed related to the D. When Whitebeard was recalling his conversation with Roger about the true meaning of the D. he stated that Blackbeard wasn't "the man Roger was waiting for." So, there's indeed a connection between Joyboy, the D. and the concept of inherited will. I mean is it really reincarnation or possession? Also, @El Hermano is it me, or it seems the DF the WG was talking about may indeed be Luffy's DF?