Ambarella released some information on the A9 SOC recently.

Considering that the GoPro 3+ Black uses the A7 SOC while the White and Silver use the A5s it would seem that we now have some insight into the possible features of the top tier Hero 4.

Of particular interest:
4k @ 30fps
1080p @ 120 fps
720p @ 240fps
700Mpixels/s oversampling

Sounds juicy