Who says that Canon and Nikon mirrorless cannot be adapted to Sony mirrorless. Just because there is no mount, yet, just implies there is just no real demand to adapt either Canon or Nikon onto Sony as Sony has a fairly complete set of lenses available to it.
I do really understand your absolute desire to paint Sony as a system superior in every possible way, but it is physically impossible to mount Z lenses on a Sony body.
Indeed, the flange distance of the Z mount is 2mm shorter and the mount is 10mm larger.
Unless the laws of mechanics change dramatically, this will never ever become possible.
The same way it was never possible to mount EOS lenses on F mount DSLRs.
Cheers,
Bernard