- inertia (don't rewrite something if it works; who really wants to own responsibility for testing this thing on all architectures GRUB currently supports?)
- multi-OS boot scenarios (I assume this new system will support that, but (a) I don't know for sure and (b) I don't really want to boot all the way into Linux just to throw Linux away and boot something else...)
Faster boot times and more secure installations are always advantageous. I'm all rooting for this development.
I've been wondering for a while why grub is still used, given that its basic architecture is outdated.