"Extracting SB9600 data from /\/\ usually involves an NDA and some KY"
Or an oscilloscope, a serial port and some patience!

There's also quite a bit of info on the web in various places but it's not all accurate and I certainly don't like the idea of firing untested op-codes at my rigs!
I can only do modules for the radios I own so I might take a look at GP688 this weekend. That should give us a rough idea of how different they might be between models. (I already see a difference on the wire - there's no BUSY signal on the accessory connector so the timing may be more important.)
We will end up with lots of different radio modules, but maybe there will be some common elements which we can split out into their own modules for reuse. Such is the power of object orientation. The end result could be a really useful library for testing, hobby use, building new applications, etc - or it could just be a bit of fun. Either way I hope someone enjoys it.
Also of interest is the EEPROM format... but I bet that info is more secret than even an NDA and KY can provide! Perhaps some enterprising person with access to the software can write a load of different EEPROM files with it documenting the differences - who knows? Is that even possible?

Anyway, that project is for another rainy day.