Minor nit. The ELF file format is not limited to Linux. AFAIK it’s also used on FreeBSD, OpenBSD, Illumos (there may be others). It also is the target for many embedded toolchains (firmware gets built into ELF files before being converted into some final binary for flashing).
Regardless, super cool exploration.
Haiku uses ELF, as did BeOS - but, interestingly, older versions of BeOS used the PE (Portable Executable) format. PE is what Windows uses, but it’s pretty much only Windows/Windows-workalikes and UEFI that use it these days, IIRC.
I thought it used PEF, which is what the classic Mac OS used.