Nikon confirmed that the new eye-detection AF firmware update and more for the Nikon Z6/Z7 cameras is scheduled to be released next week (May 16th). This timeframe matches with my previous report of a CF Express firmware update for the Nikon Z cameras to be released in the second quarter of 2019.
I received a rumor that the upcoming firmware update will also improve low light focus capability to -6EV for the Z6 and -4EV for the Z7.
Nikon announced the development of new firmware for the Z6, Z7, D5, D850 and D500 cameras