  The hypothesis that every theory of quantum gravity in AdS_3 is a dimensional
reduction of string/M-theory leads to a natural conjecture for the density of
states of two dimensional CFTs with a large central charge limit. We prove this
conjecture for 2D CFTs which are orbifolds by permutation groups. In
particular, we characterize those permutation groups which give CFTs with
well-defined large N limits and can thus serve as holographic duals to bulk
gravity theories in AdS_3. We then show that the holographic dual of a
permutation orbifold will have a Hagedorn spectrum in the large N limit. This
is evidence that, within this landscape, every theory of quantum gravity with a
semi-classical limit is a string theory.
