Make use of Containerization for generating the images. This will allow users to generate images for Fedora Versions that they aren't running on their host PCs and will generally make the process of image creation host-agnostic.
The image generation (i.e. probably running Lorax) will then take place in the Container.
osbuild, according to its own docs, only supports building images for the same arch and os-version it's running from! Thus to make an image for aarch64 from Rawhide, we'd probably have to boot Rawhide on QEMU.
I'm no expert on QEMU, so I'll see if I find another way to make the images instead...