Sure, GR may well be self-contained and cannot encompass the quantum world in the same sense as the Newtonian mechanics is and can't. But the Nature does not have such boundaries, especially at such a fundamental level, and it is "self-contained" as a whole. So, while it may be impractical to try an create a unified theory of some aspects of reality, say, quantum mechanics and linguistics or economy, theories concerning fundamental aspects of Nature naturally are, and have been, subject to unification.