Everything is for sale. Thats not to say Zeiss would not insist on involvement.
What surprises me about the whole G Master exercise - other than the dreadful comic book hero name, that is
- is Zeiss now become the mid-range lens choice, not the top of the range they like to be. Imagine the conversation "gee, I'd love to buy that G Master lens, but I'm going to have to make do with the Zeiss..." !
My entirely uninformed guess about this is that Sony might have thought (rightly in my view) that some Zeiss lenses for E-mount are over priced and frankly mediocre. Sony must have felt they could do better and that the mount was being held back by Zeiss with lenses like the 24-70 F/4. Sure Zeiss could up their game but the cost would be too high.
Also, Sony as a major innovator would not want to be dependent on a third party to make its premium lens range. Still, Zeiss have been useful to Sony, adding credibilty and some breadth to their lineup.
Some Zeiss e mount lenses are excellent, of course but not enough and nor are they under Sony control.