I talked to some Nikon reps yesterday, and got some tidbits that may be of use to my fellow Z enthusiasts:
Firmware on track for the 16th of this month - eye AF, etc.
This firmware may not contain the CF Express update.
When the CF Express update comes, the cameras will be able to recognize both XQD and CF Express cards - just stick a card in and the camera knows what it has. It won't require switching anything in a menu, and it certainly won't make XQD unusable.
And from a memory card manufacturer rep: CF Express cards will be out "a few weeks after" the firmware update that enables them, and about 20% cheaper than XQD.