Since DebConf 17 I was working on cross-architecture support for FAI. The new FAI release supports creating cross-architecture disk images, for e.g. you can build an image for Arm64 (aarch64) on a host running 64-bit x86 Linux (amd64) in about 6 minutes.
The release announcement has more details, and I also created a video showing the build process for an Arm64 disk image and booting this image using Qemu.
I'm happy to join the Debian cloud sprint in a week, where more FAI related work is waiting.