Thank you, Tom,
In fact I just made a rough memory map earlier today, just studying the memory dump file from the memory card with a hex editor. When comparing my guesses with the mapping used by the FTM-350 module most major stuff seems to be in the same places. There are new features and settings, of course, and I will have to sort those out, but I think I can use the FTM-350 module as a starting point.
Of course, one difference is the two different ways of accessing the memory, cable or card.
I have not found any way of making the radio save more than one incarnation of the memory dump, alas.
One possible interesting (non Chirp related thing) about it is the optional camera microphone, which connects (for the camera) to what looks a lot like a mini USB B, and where such a cable also fits. What if it would be possible to connect some simple webcam instead of the more expensive Yaesu cam mic. :-)