Not useless, it's a useful thing to have when you're trying to learn how to write Hello World as an OS - http://wiki.osdev.org/Bare_Bones

Are there any bootloader specs that are standard across architectures? UEFI comes to mind, and I'm sure you could boot an x86 board via u-boot.

Actually UEFI was very Intel-centric when it started out. It worked only on Itanium and x86. We (Red Hat) spent a great deal of time of a very talented colleague of mine porting it to Aarch64.

Aaaand the jawdrop happened when I reached the last word in that sentence. Wow, kudos.

Know of any cool videos or anything similar that demo UEFI functionality on AA64?

I'm afraid I don't have any videos. If you get the APM Mustang, it boots into UEFI.

...ah, nice price (fair, but decidedly not RPi or CHIP scale). Mentally noted, at least :D