grub-install fails if the filesystem on which it is installed is not FAT:

if test "x$fs_module" = xfat; then :; else
    echo "${grubdir} doesn't look like an EFI partition." 1>&2
    exit 1
fi

I have grub installed on an HFS+ partition on my Mac, because I don't want
to use the fragile FAT filesystem for the bootloader.  This works fine, and
I can read and write the partition in Linux and OS X. The EFI spec states
that the boot partition should be FAT. However, upstream told me that the EFI
support in grub-install is mainly targets Mac support, and Macs can also
boot from HFS(+) partitions. It would be nice to have support for this in
grub-install.

Regards,
Tino

severity 589902 wishlist
thanks
HFS(+) way is Apple-specific, distinct from standard way and is poorly
documented. Moreover Apple systems are bootable the standard EFI way and
by default it has EFI system partition which would otherwise be unused.
So advantages of using HFS(+) are purely theoretical. Decreasing severity