As someone currently working on supporting application and firmware code on this platform, this is pretty interesting. I'd also like to point out that Buildroot

As someone currently working on supporting application and firmware code on this platform, this is pretty interesting. I'd also like to point out that Buildroot (https://buildroot.org https://buildroot.org) and upstream U-boot have first class support for building and running your own 64-bit kernel and userland based on included defconfigs. If you have an application you'd like to ship on a Raspberry Pi image, especially if you want to address all 8 GiB from a single process, check out Buildroot.