Yes, the eye AF function is now present [in a4]. But I've yet to try it on a human. There is Technical Service Advisory guide just out:
https://www.nikonusa.com/en/service-and-support/service-advisories/technical-service-advisory-for-users-of-the-nikon-z-6-and-z-7-cameras.htmlAnd this video on setup and tweaking the new Eye-AF mode:
https://youtu.be/RPJHDSOFD5cShutter blackout is much less shooting High-Continuous. In d5 you can now set Shutter Type to 1 among a choice of 3. Not only Mechanical or Electronic but also to 'Auto', in which the camera selects Shutter Type based on shooting conditions. I haven't yet found out what the thresholds are, but previously set in Electronic mode it was not possible to select faster than 1/2000. In Auto this upper bound is removed, obviously.
Scrolling through the Custom settings, this new Firmware hasn't updated customization options - these are limited wrt critical functions. This cripples my Z7 in key respects. For one, unlike a D850 (or D500) I cannot toggle between the AF setting on to an alternative AF mode [eg Dynamic-Area and Single-Point]. Playback menu settings remain limited; they are still not segregated from Photo Menu. So setting the Fn button to Image-protect in Playback makes it useless, as it cannot be set to a complementary custom command for Shooting.
While it's great to see Nikon coders have focused efforts on updating a feature in AF, they have not acted on the intense effort first Z owners expended in feedback on forums etc to prioritize straightforward fixes. So the message many customers will take from this is, "You do not matter." Sad