Reading this as a layman, it looks like releasing ΛCDM's cosmological principle [1] reveals the nontrivial temporal effects mass clusters have via general relativity. As a result, there could be empty regions of space in which billions of years more have elapsed than in e.g. a galaxy. This not only changes how we interpret supernova data (the acceleration isn't generally happening, but an artefact of looking through space which is older than our own), but may also negate the need for dark matter (EDIT: dark energy) and the meaning of a single age of our univese.
(I'm also vaguely remembering a multi-universe model in which empty space inflates quicker than massed space.)
(I'm also vaguely remembering a multi-universe model in which empty space inflates quicker than massed space.)
[1] https://en.wikipedia.org/wiki/Cosmological_principle