My understanding is that there isn’t much point theorizing about the “outside” universe beyond the horizon of our light cone, because there is no present or future interaction possible between it and us.
There’s good reason to theorize about it. Theories might be able to point to or estimate the size even if we can’t directly measure it. For instance if we find evidence of inflation in more fundamental physical processes, we can assume there’s more universe out there than we can see.