I find Smolin's ideas including CNS connected to a multiverse interesting. Boltzmann brains always seemed ridiculous because a brain needs an environment to provide it energy and protect it. In practice a body to hold it, a surface (planet or moon) and large energy source (star).

Gravity is not always attractive, of course, dark energy, more correctly, the dark negative pressure associated with dark energy enters in the stress-energy tensor and is a push or negative gravity rather than a pull.

P = -w ρ c^2 is the equation of state, (dark pressure, EOS parameter, energy density) and since the P gets a factor of 3 in the stress-energy tensor, if w < -1/3 for a component, then the sum of P + ρ is negative and the overall contribution of dark energy results in an acceleration of the expansion (if dark energy exceeds dark and ordinary matter). Of course we observe w ~ -1, the simple cosmological constant version.

The universe produces other than black holes because the primordial density fluctuation spectrum spans many orders of magnitude of mass scale, one has to produce stars of various masses. This is just observational fact. And large mass stars that supernova recycle preferentially to lower mass stars. Given the much longer lifetime of low mass stars relative to high mass progenitors of black holes, they dominate more and more and collect most of the stellar mass.

n.b. I had the same thesis advisor at Harvard, earlier than Sean Carroll (George Field). Sean is smarter.