Perhaps the science is not completely unifiable for a very logical reason. Perhaps unification and finality would render the science “somewhat un-scientific”. A complete GUT of Everything requires a completely Platonist interpretation of Mathematics and mathematical science— mathematical rules, axioms and definitions must be objectified to preexist before all other existence. Such a theory that accounts for everything including its own existence seems as potentially fraught with voodoo as any metaphysical or pseudoscientific counterpart. The theologian’s ‘God’ becomes the mathematical physicist’s equation and that equation is essentially a self-perpetuating tautology that somehow can be broken down and reassembled by scientific minds whose very existence it is responsible for in the first place. It is the Cartesian “I think, therefore I am capable of thinking that things that think can think that they exist” (paraphrased)
To me, an asymmetric gestalt of theries would be much more logically and scientifically satisfying and much less voodoo-dependent — two different yet co-dependent theories explaining two different yet co-dependent entities; mass-energy and Spacetime. And this arrangement would also seem much more in coherence with Godelean mathematical incompleteness as well as the observation that a continually evolving Universe does, in fact, appear to exist.
My personal guess is this:
The current Standard Model depends upon random quantum fluctuations and these throw a bit of an “uncaused causation” into the mix, especially in the absence of “observers”. Perhaps it is that a separate and non unifiable theory of gravitation and spacetime is necessary to provide that missing causation for random fluctuation and spontaneous symmetry-breaking itself. My guess is that our current interpretations of Einsteinian Relativity are not entirely correct and that something akin to Hawking “imaginary time” is at work. The Big Bang did not necessarily create spacetime but merely gave spacetime a measurable form, and it was the formlessness of pre-Bang spacetime that provided the potential for the Big Bang quantum fluctuation. Formless chaos is inherently unstable, hence the bang…