I went ahead and ported GRUB to Sortix.
I prepared a nice disk image with a full installation of my OS and the GRUB tools and files, but the disk image has no bootloader and won't boot. I then used a grub rescue disk to manually boot the kernel and initrd on it. I check the geometry of the devices, locate the root partition and the root disk, then I install the GRUB onto the root disk. Finally, I generate the bootloader configuration so it boots offers a splash screen with an entry to boot /boot/sortix.bin and /boot/sortix.initrd.
I power off the system, remove the GRUB rescue disk, and just am left with the harddisk image. I boot it up, and I get a fancy GRUB splash screen offering to boot my OS:
And it even works! (This is grub-2.02~beta2, the stable grub-2.00 I first ported was too buggy to boot my OS.)
Oh hey. That actually also ported grub-mkrescue. I gotta port xorriso and complete Bare Bones one of these days.