I just want to say that I am so happy about this rumor. I really like Sigma lenses and I have not yet found a camera that suits me with E, L or Sigma mount. Now I think my future mirrorless mount will be Z or RF mount, probably with a slight Z mount advantage, but I follow all developments.
I hope the rumor is true. I trust that if it is Sigma has already made sure that AF works great. I also hope that it will bring more photographers to the Z mount and will make Nikon stronger overall.