Nikon's roadmap doesn't contain any really long lenses.
At present appear to Nikon target the Z cameras for applications and users who benefit/prefer from compactness, smaller size, short focal length lenses that allow benefits to be gained from the new mount. Applications such as portraits, travel, landscape, video seem to be emphasized, not wildlife action or sports.
Their intention is to develop F and Z systems to take advantage of the benefits of each technology. I.e. they will make Z cameras and lenses that take specific advantages from the mirrorless technology and F mount cameras and lenses that take advantage of the DSLR technology. At present I suspect Nikon consider that the DSLRs are better for telephoto action than the Z cameras, and user reports also suggest the AF tracking of moving subjects in the Z isn't at the level of the high end DSLR. So why make expensive new lenses that don't work as well as F mount lenses (on F mount cameras?) for the intended applications? I think the camera technology needs to be developed to such a level that this type of lenses make sense to design. (Yes, I understand the Sony A9 but it is not clear if Nikon can do that.)
Is it difficult for Nikon to "convert", that is to redesign these two lenses, to work natively on Z-cameras?
The FTZ seems to be designed in such a way that it is robust and feels like one piece with the camera, so there probably isn't too much disadvantage from using this with F mount lenses instead. If a lens is "converted" to another mount then it cannot be used with the F mount cameras after that, which may reduce its resale value given the large number of F mount cameras in use. To take advantage of the full feature set of the Z cameras, new motors and electronics would need to be designed and implemented in the conversion so that AF works optimally, and the motor solution is also tied to optical design. Even though Sigma offers a conversion service the cost is such that it is probably more sensible to sell the lens and buy a new one for the mount you want for most lenses rather than have the conversion made. Also it doesn't seem that they really optimized the new E mount versions for the E mount in such a way that would be done if they had started from scratch. I think Nikon will want to make new lenses for Z mount from scratch to take optimal advantage of the new mount and the cameras' features rather than offer a conversion service.
