All right, at the end of KH: CoM Reverse/Rebirth, we see an illustrated scene of BHK looking over at Twilight Town. When I think about this scene another thought came into my head: "If BHK is Sora's shell alone, why would they show that scene at the end of R/R?". I came up with two conclusions: either they put that scene to make fans happy, or BHK is not only Sora's shell, but Riku's as well. Why else would BHK be able to wield two keyblades? Because he's the shell of two people chosen by the key, one for the darkness (Oblivion/Riku) and the other for the light (Oathkeeper/Sora). It could also explain why BHK is blonde, a mixture of the white/silver hair of Riku, and the dark brown brown hair of Sora. And lastly, the boxart, the face of the BHK in that picture, didn't remind me of Sora, it reminded me of Riku.