This is incredibly interesting, and I can't really wrap my head around it. In a way, such "Boltzmann Brains" would be similar to "Tralfamadorians" from Kurt Vonnegut's Slaughterhouse 5. This would be with regards to their lack of an "arrow of time". Everything would be, and everything would not be. As to the actual formation of such a thing, that's where I'm completely lost. The other issue I'm having is what exactly a post black hole universe would be like?