I feel like your best bet with this would be one of the kexec-based bootloaders, because then it's a "real" Linux environment there, with whatever tools you wan

I feel like your best bet with this would be one of the kexec-based bootloaders, because then it's a "real" Linux environment there, with whatever tools you want in it, instead of something special. Eg: https://github.com/kexecboot/kexecboot https://github.com/kexecboot/kexecboot