Tokina confirmed to me that they currently have no plans to make mirrorless lenses for Nikon Z-mount. Tokina already has several mirrorless lenses available for other mounts.
Sigma is still talking about Nikon Z mount lenses but it is not clear yet if Nikon will be ok working with another manufacturer. Reminder: over the years Nikon has filed at least two patent infringement lawsuits against Sigma.
It seems that for now only Tamron and Cosina have the official blessing from Nikon to produce Z-mount lenses.
