I'm pretty stoked about the new 4k gopro. I'm thinking of using them for unattended stage right and left recording. Basically suction cup them to the auditorium walls and then controlling them via laptop. I don't like the wide 180 view, but figure I can pan 1920x1080 around where I need it to avoid he fish eye.
I was thinking of the lens kit also, but would rather wait and see how others make out. My main concern with the lens kit is loosing low light performance when you add a bunch of lens elements. Also, would I then have to rely on manual focus.
I stand to be corrected, but AFAIK the standard GoPro lens does not have any moving focus element, nor iris. There are some very fast CS mount lenses available, one is f1.4 that I looked at
The disadvantage of the lens kit is that you do not have a waterproof camera any longer, but this is not so much of an issue to me.
If you only want to use 1080 mode, then you can opt for the 'Narrow' field of view, with must reduced distortion. GoPro claim the new lens is better distortion wise anyway.