This is different to what I was talking about -- your link is about running Emacs as pid1 on Linux (cool, but not particularly innovative -- if you run Emacs in a Docker container that is effectively what you're doing). I was talking about booting from UEFI into Emacs, without the Linux kernel at all. Given that there is a glibc port for UEFI that uses just BootServices it would be very possible to do this.