This is an interesting proposition that there exists an one single theory what he mentioned as 'theory of everything.' One thing popped up in my head immediately: if such a thing exists where should we look for? or What is the nature of such a thing? What are the characteristics of that theory? My question is even more philosophical I guess! I think I would like to know what are the characteristic the 'theory of everything' must have to consider as a theory of everything? Now the question is there anything exists like that?
Well, I can play an interesting trick David Deutsch played at the beginning of Fabric of Reality. Let say such a theory exists, and as I understand, the only existence of any theory is through its interpretation. I presume there would be numerous interpretation of such a theory. There would be medical science, physics, chemistry and so on. All these are interpretations of that same unified theory. Now can I say like David Deutsch' Oracle, that such theory indeed exists which is our universe! Universe is the theory that has numerous interpretation in our life.
My second concern about such a theory is even more philosophical. Since he didn't defined the characteristics solution, why some philosophical ideas would not be qualified as candidate solution! One such a solution indeed exists in the history of mankind for many year: religion. Religion indeed presents one single unified theory of everything. What makes the proposition even more interesting is, all consequences and existing phenomena may not be immediately understandable from the theory. Just like, it needs years of work to explain real world using our existing theories, we need years of work to explain this universe using religion as well. On top that, religion is upgrading day by day. My proposition is: nothing disqualify a religion as a candidate for the theory of everything.