In the previous post, I mentioned Marni Sheppeard's theory of mass, as arising from an interaction of ordinary and mirror matter. She also recently posted a sketch of her cosmological ideas. They are sort of mysterious, but they may make a little more sense if you've seen Christof Wetterich's recent work on "A universe without expansion", which almost seems to be saying that whether the universe is expanding is a point of view - you can change coordinate systems, and also rescale certain fields, and the universe might be static, or even shrinking, depending on what picture you have adopted. Sheppeard's universe seems to be static, but baryonic mass and mirror mass change over time, and this gives the appearance of expansion. Or something like that; this post isn't about her cosmology, but I mention it because it's in the same territory as what follows. (An Iranian review of nonstandard cosmologies may also be of interest.)
More recently, I was reminded of a problem I have with Wetterich's concept - doesn't it require baryonic mass to vary with the VEV of his "cosmon field", in a way which is not consonant with the complexity of how mass is actually produced in QCD? As of this date, the comments beneath my question say that Wetterich's idea is just about trivial rescaling of the metric, but I don't think that's correct, I think its viability depends on there being a certain mechanism of mass generation as well. I note that Wetterich has tried to produce a Higgs-like effective theory of QCD, and perhaps he was motivated by this very problem.
But here is today's idea. Let's suppose that Wetterich's scenario works after all. Could it even be applied within anti-de-Sitter space, so that the cosmic geometry is really AdS, but the evolution of the mass-generating cosmon field produces the appearance of universal expansion? (I owe this concept to a conversation with A. Hattawi about Wetterich's ideas, and a conversation with T. Seletskaia about applications of AdS to cosmology.)
I could also go further and mention A. Rivero's latest speculation, about dark energy as the slight positive excess remaining from a near-cancellation of AdS negative curvature, and the vacuum energy arising from a Higgs VEV. (Also see posts here, 1 2.) And if you want the perspective of people who know what they're talking about, see e.g. Polchinski and Silverstein, page 5, for the three different contributions to the vacuum energy of a typical Freund-Rubin compactification (AdS curvature, curvature of KK-like compact dimensions, energy densities of stringy fluxes).