This kinda sounds like zfsbootmenu but without the ZFS. Which makes me wonder how hard it would be to factor out the ZFS bits and just use zfsbootmenu on other filesystems.
It'd be doable, but not with out a whole lot of hacking on it. The internals of ZFSBootMenu are tied very tightly to ZFS. Though at that point you'd largely be reimplementing https://github.com/open-power/petitboot - which probably would be easier to port to x86_64 as an EFI application.
