RaspberryPi.org has, months ago, published a ROM update for the RasPi4 that allows USB booting.
This works out of the box with the 64-bit Raspian OS.
The RasPi Kali distribution however doesn?t work with this.

I used to be able to get this to work, by selectively copying the start* and fixup* files from a Raspian image into the boot folder of the Kali image.

It seems however, the lastest kernel update has broken this, good chance I?ll get it to work with hacking around for a bit, but given how much faster booting and operating the system is over a USB3 connected SSD, I?m a bit surprised that the USB boot functionality hasn?t been picked up yet, or am I missing something?