As my head's now out of the weeds and back to the vision, thinking ahead: if the RPi Kernel fork is going to be required long term, it'd be beneficial for the Slackware on RPi community to converge on a known-good set of firmware and bootware.
Even if you want to run the RPi Kernel fork on your RPi, Slackware AArch64 can be installed following the
documentation. Once the OS is booted, one can use 'upgradepkg' to switch to the RPi Kernel fork.
Although it's not recommended nor documented there, you can install the OS to the Micro SD card if you wish. You'd probably want to use the
'bare' Installer images though, and we can update the Install guide to explain how to install over the LAN or from a USB stick (as was the procedure in the intial public release). The older version of that documentation is still available and can be merged reasonably easily.
All that would be required is to provide an new Kernel package built using
this procedure.
The RPi components within Slackware (Kernel firmware, boot loader and default configs, 'bootware' (DTBs, propriatory 1st stage boot loader & stuff), EEPROM firmware) can be maintained by people within the community: interested in the firmware (some people are ;-) ) ? tried a new version for a while and found it stable? drop a note to the forum, along with any fixes/changes. I'll fold it back into Slackware.
This is just an idea. I'm not in love with RPi's for numerous reasons, so updating its firmware is low prority for me. Some of you love them and I'm happy for you to contribute back into the project.
moment. I read your post and wrongly assumed you were giving me a hint to release some SARPi3 updates. I thought "What is he talking about? I've just uploaded a new batch! 
