I don't know if it's intentional or not, but /camerashake (both positional and rotational) doesn't work while using the new /camera (minecraft:free) command. 

Here's the video to guide
camerafunny.mp4
 

Steps to Reproduce:
1. Turn on the experimental /camera command setting.
2. Use the /camera(minecraft:free) command.
3. Use the /camerashake command, and done.

Observed Results:
Nothing happens even if you used /camerashake.

Expected Results:
It should ACTUALLY shake your camera like in this video. (I didn't use "/camera" while recording this video)
camerashake.mp4