'aight, n'uff said. Maybe this could be a canon, but I guess personally I just don't agree with it. But whatever, just my opinion.
Since we haven't met anyone within the backrooms who isn't from our own universe, each universe probably has its own version of the backrooms(unless they are unware of any minor differences between theirs and our own universe). So the backrooms wouldn't be inbetween any other universes, and therefore would not be a hub.
I don't think that would be the backrooms anymore, it would be some other world. The backrooms is an unreality, not a multiversal hub. You could make one if you want, I just don't think it would fit in this wiki, as it would provided a form of escape, maybe you could put it on scp wiki tho.