Here's a video that I just found out (even though it was released on Dec 9th last year):
Here's some conclusion I got from the short vid:
1. Waterproof case is BADLY ENGINEERED.
Just see the video, I lost my words. Waiting for a good 3rd party maker then.
2. Charging case is really using the adapter pins.
Now we just need some 3rd party adaptor hack to create a charging adapter so we can use the adapter port to charging via external source while OP is using 3.5mm audio adapter.
EDIT:At first, I put that extension rod have a wifi capability. Turns out the OP mentioned here is using wifi module. So sorry.
Now I wondered whether the extension rod have a battery of it's own and having the ability to charge the OP while it's docked. That'll be awesome.
limited visibility, that would really hinders the recording.
You see, at the video, the recording even got blocked.
I really wonder why DJI don't create a dome-like waterproof case that could use OP's gimbal rotation better.