After countless of hours of trying and lots of my kexec calls getting oom killed, i finally managed to install #NixOS on a KVM server from st-hosting.com. Even unlocking the hard drive via ssh in the initrd works. The whole thing was certainly a learning experience.

#nixos-anywhere is amazing.

I think i will have to find out why kexecing into a less than 500 MiB image takes over 1 GiB of memory tho. There has to be a bug there somewhere.