I feel like that post misses the biggest one that pulls people to GRUB: complicated boot sources and procedures. Filesystems that UEFI doesn't understand, more complex network boot sources, all that kind of complex messiness that GRUB enables and others don't. Now, whether those are good idea or not is a different question, but I think this is a good concept for a full replacement for GRUB, as opposed to the existing replacements which already cover the 90% case pretty well. (And I think it's got a case for handling the other cases OK: from the sounds of it they plan to lean on UEFI and A/B image to handle fallback, and it'll basically just work as a direct UEFI boot in the common case)