I was thinking the same thing about cameras when I read the post. It seems like a lot of the fatigue issues have to do with being too "present". In a days-long conference setting, I think I'd feel the same amount of extra energy loss as video conferences. Even "cognitive load" and "reduced mobility" could be managed better with your camera off in a video conference. When I have my camera off, I am more free to zone out, fidget, and do a number of things I could do in a conference room that I might not feel comfortable doing with my camera on in a video conference.