So, we had a planned I1 firmware release pulled back around the 20th of June - followed by calls for a new round of Beta testers around the start of July.
It's now a month later - what is going on? Is there any sign of something vaguely resembling a new firmware/app version appearing?

Many 3rd Parties are testing products themselves, but no real indication of proper GS, waypoints or Nav as yet.

Or are the DJI techs busy with a Phantom 4? S1100? Matrice 2?

Beta tests are still ongoing.. That's all anyone in beta test will tell you

DJI keeping us like well tended mushrooms.
Kept in the dark and covered in ...

Guys I would tell you a lot more, but since I have NDA All I can say is that beta is still in test phase.