As far as we've seen there is only one Kamui Dimension if there is a specific one per set of eyes then the person could in theory either go to his/her own dimension from another persons dimension or to Earth.
It all depends on whether the Kamui Dimension(s) are per Eye set or to the jutsu in general... we'd have to see Sasuke, or Madara use Kamui in order to determine which is which. It would make sense either way; One dimension or Many.
Very interesting idea... it would add a very weird element to the cosmology of the Narutoverse.