hi bpv5P,
the encryption causes writing speed to go drastically down.
a simple repeaing XOR key which is not even halway safe, causes a drop in write speed by factor 2 or so?
so any real cipher makes life really hard 
possible - but practical?
Yeah, I don't know the solution.
Here's another idea: get the camera "MAC address" (I don't know if it's called that way on such devices), and encrypt the DNG metadata using it. It could be useful for legal usage, so you can autheticate the image. RAW image alone is used today as legal evidence, but it can be easily edited with the right tools, preserving metadata.
Although the idea above could be useful for some people, it will not be worth for journalists, for example, since anyone could see and delete the picture.
Another solution could be use homomorphic encryption on Wifi cameras:
https://tfhe.github.io/tfhe/Or maybe to encrypt the whole
filesystem with
Chacha20, that's a faster algorithm than most of the ciphers...
I don't understand all of these concepts, though, I'm just leaving some links in case you have time and will to research...