Oh dear. It's another firmware update issue. I'm have a script to fix the compatibility, it also removes the firmware update. You can try that
here if you want. Let me know if you need help with something.
No working 10.14.4 beta - but different story here: OTA worked well, no firmware update issue, but after reboot (and re-patching with the v1.2.3 patcher) I get a "non supported machine" error.
Strange thing: The PlatformSupport.plist has valid entry for my MBP 5,2 (as before!), as to be expected when applying that particular patch.
There must be some other location (perhaps the EFI boot volume) with another plist file to be modified. Will continue to look for it...
EDIT:
No luck, found no other location containing a PlatformSupport.plist file. So this is no different to previous 10.14. Mojave versions.
Two more observations, though: Tried the OTA 10.14.4 beta 1 on two more machines, one MB Pro 4,1 and one MB Pro 7,1. On both, the "unsupported" message did not show up, but near the end of the booting process, graphics switched back to log text output and kind of cycling through the messages shown in the photo. I´d regard them as GPU/graphics-related.
Cycling means, blank screen for a few seconds, then again text msg output for a few seconds, always same output. 2nd photo shows non-verbose progress and stuck point near end. Spinning wheel also not correctly rendered for some reason, completely white after a while.
At this point I assume that
@dosdude1 and his patcher magic in a new version of the tool will be necessary... ;-)