With my background on the Commodore Amiga and the 32-bit IFF format, the visual approach is more appealing than a text-based format of any sort. Though having to use a hex-editor to debug a format, it’s not much different than using a text-editor without syntax highlighting. Plus, once the new format is ready, the editor will be more visually appealing than any text editor could ever render, even with syntax-highlighting.
The best balance would be to have keywords as text and nesting levels of structures as a graphical collapsible tree gadget. Trying to make a text format humanly readable is not necessary but taking less space on disk and time to parse is preferable. If HRD is more compact than XML then that’s great but the humanly readable aspect of it doesn’t look so hopeful to me. What I hope for is that BSON would be to JSON what the new format would be to XML.