I can now confirm that Nikon will indeed announce a new lens next week that will not be from the existing Nikon Z roadmap.
Nikon will announce another rebadged Tamron wide-angle zoom lens.
From the list of Tamron mirrorless lenses that could potentially be announced for Nikon Z-mount, I think the most likely scenario is one of the following lenses:
Since Nikon already has the Nikkor Z 28-75mm f/2.8 lens (the first rebadged Tamron lens for Nikon Z-mount), maybe next week we will see a new Nikkor Z 17-28mm f/2.8, but this range is too close to the existing 14-24mm Z lens. The best option is probably a new Nikkor Z 20-40mm f/2.8. What do you think?
The official announcement is expected on Monday or Tuesday night. Stay tuned for more details. Of course, all these are just rumors collected from multiple sources and some information could be wrong.
Please note that I expect a new Nikon Z rebadged Tamron lens and not a new Tamron lens for Nikon Z-mount. A few weeks ago Tamron announced their first lens for Nikon Z-mount – the Tamron 70-300mm f/4.5-6.3 Di III RXD and I am sure there will be more to come in the future: