The part of this that stands out to me: the OS claims to be open source. But the bootloader is proprietary. Why? Does the source depend on proprietary specifications that have been embedded in parts of it or something? The documentation doesn't obviously preclude writing a replacement, but nor does it seem to be designed to encourage such a thing. On the surface it's not complex enough for this to be a huge task, but I'm suspecting there's at least one strange grinding obstacle in the way…