well, if you want to talk philosophy...

a 'theory' of everything *is* possible, but a theory by definition is between a hypothesis and a principle. A theory works until it breaks down. You can have theories for anything, but you've gotta test them. If you can't compute the theory though, it breaks down into a new hypothesis, or if it holds up enough over time that the general consensus is that it's true, then it becomes a principle.