"An interesting possibility, which I think should not be dismissed, is that a "true" fundamental theory exists, but that it may just be too hard for human brains to grasp. A fish may be barely aware of the medium in which it lives and swims; certainly it has no intellectual powers to comprehend that water consists of interlinked atoms of hydrogen and oxygen. The microstructure of empty space could, likewise, be far too complex for unaided human brains to grasp."

That's a distinct possibility. Further mathematical research might still allow considerable refinement in describing what a correct fundamental theory does NOT imply.