I think I know the answer but....

What is the USB plug for on the back of the P34k remote?

To connect your iOS or android device for fpv from the bird's camera.

Or to connect a USB drive with firmware updates, most are done with wifi now though to be fair. I don't think the USB on the 4K will be redundant entirely though.

stray_bullets Posted at 2016-2-11 23:56
To connect your iOS or android device for fpv from the bird's camera.

The Phantom3 4k does not work like that. The FPV is done via WiFI and not through the USB cable like the Pro/Advanced are.

The USB port on the back is reserved for future use.

Thank you Ken,  

I love my bird but boy...  there is a lot of confusion on P34k and P3P with 4k...  But I get it....

DJI-Ken Posted at 2016-2-11 16:02
The USB port on the back is reserved for future use.

I see, thanks for the info

stray_bullets Posted at 2016-2-12 00:27
I see, thanks for the info

No problem, page 9 of the manual explains it