I've always liked that theory, because, at the moment, Dragonsteel just kind of exists. Given metal's significance in the Cosmere, I wouldn't at all be surprised to find that Dragonsteel is Adonalsiumium (Try saying that 5 times fast). Of course the fact that I wouldn't be surprised by it being one and the same, means that Brandon probably knows that we wouldn't be surprised and it's a red herring....