It makes no sense to offer a premium product with Sigma/Tamron reverse autofocus and something that you can't even guarantee will work as you intended it to in the coming years. I'm sure if Zeiss can make £25k master primes with ARRI it could give the reverse engineering a go, but if I was them I'd either be all in with Nikon and Canon or not bother to save tarnishing the brand. Essentially by granting permission to interface with the Nikon AF and electronics you are cooperating, and by not granting permission you are uncooperative. Can't have one without the other.
The Zeiss lenses will always have a market though, they offer some of the best lenses you can get in F mount for photography or video work.
If Zeiss required permission then they would be sued since according to your logic Zeiss are selling lenses with canon's or Nikon's permission. No permission is required to produce a compatible lens.
Secondly, your opinion on the quality of sigma AF is extremely dated and not at all a reflection of the current state of the market.