There isn't really documentation for the new format yet because it's not yet been officially released. If you do manage to download the firmware updater you'd be the first person outside Pycom to actually use it. And as I said before it's still experimental and I'm aware of some issues with it such as the otadata partition definition missing, so please don't try to modify the script2 file in a firmware package.
I'm still in China this week and things tend to get more and more hectic towards the end of the trip so I likely won't be able to do any work on the firmware updater until I'm back in Eindhoven.
@crumble I forgot to mention it in the survey, but a download feature would be extremely handy since my devices are rarely if ever on WiFi, and FTP requires extra steps to configure wifi on the board I'm testing.