Is it though? It is my understanding that the quantum fluctuations that give rise to BBs will still exist, even after (and specially after) the evaporation of black holes (perhaps assuming no Big Rip).
If so, does this theoretically mean that a cyclic universe is possible in this way, and that if one were to go far enough - impossibly, unfathomably far - you might find the remnants of other universes?
To dispel a misconception: They're not some hypothetical type of brain that exists as pure quantum fluctuations (though those are even more likely). Boltzmann was talking about the probability of actual flesh-and-blood human brains arising spontaneously out of the vacuum.