Just a comment RE: no documentation for how UEFI loaders would work.
I'm not sure I understand what you mean by this. Searching "uefi documentation" on Google yields a ~3000 page PDF, and looking through its contents, it seems to have more than enough documentation to make a simple chain loader for a kernel.
Has anyone tried looking at Linux, sel4, or ReactOS?
I Understand it's a total PITA to pull apart a huge system, but it's probably going to be a heck of a lot faster than combing through various technical docs and posts on osdev.
From my experience so far, it's very difficult to learn anything from the codebases of large operating system projects. Posts on the osdev forums/wiki and decent technical documentation PDFs usually seem to me to be more informative than existing source code. There are usually careful design considerations in existing projects that are lost on the uniformed reader (and possibly bugs as well), so I would have to disagree with this approach.
(Apologies if any of this sounded rude; I'm typing this post on Android and its lagginess is annoying me.)