As if on cue**, Tamron today announced they are going to bring their 70-300mm f/4.5-6.3 (Model A047) to the Nikon Z-mount some time in the fall of this year. This lens is already available for the Sony FE mount cameras, and is promoted as the "lightest and smallest tele zoom for full-frame mirrorless cameras."
Lightest means 19.2 ounces, smallest means 5.8" long. Note that while the lens doesn't have Tamron's image stabilization, it does keep Tamron's 67mm standard filter size. In using the lens briefly on a Sony camera, I found the telephoto end of the lens pretty darned good, with the weakness optically being at the wide end, where there's a strong fall-off of sharpness past the DX (APS-C) frame.
I've added the lens to the database, but it's possible some details will change slightly with the Z-mount version. I'll update the database as I learn more.
Update: I'm told that the Tamron roll-out of lenses will be slowish. Don't expect any of the high-demand and recently-announced lenses any time soon, as Tamron's production capacity is limited, and I'm pretty sure they'll prioritize the high demand ones for Sony FE mount for the time being. While it's a big lens for the small Nikon bodies, I wouldn't be surprised to see a 17-70mm f/2.8 DX lens be next.
*Yes, a play on Apple's ad welcoming IBM into the PC business.
**See my article yesterday on Canon trying to go it alone in the RF mount. Some of my comments yesterday were foreshadowing of this announcement, which I knew was coming, I just didn't know when.
