Among the de Sitter invariant states for massive fields is the Euclidean or Bunch-Davies vacuum, which allows for pair production with separations greater than the horizon distance. Since our universe seems to be marching towards a state highly similar to the Euclidean vacuum, such pairs seem (a) physically plausible (b) and with some low probability could arise in groups which (c) because they are interacting particles, might nucleate.

Nucleated objects could be long-lasting, which blunts the Boltzmann brain (Bb) picture, as under fluctuation theory the Bb is ephemeral and time-reversible. On the other hand, it's historically been attractive to think of the nucleation of a inflating patch of spacetime (with low enough entropy that structure like galaxies might form as it expands and fragments gravitationally).