Personally I suspect all the screenshots and youtubings are still "fair use" - as long as you do it to show off your ESO experience, and not try to use it in something commercial.

Usually such terms are in TOS as as... uh... rear-covering; in case someone makes something and they make something similar without even knowing what the someone made, and then get sued with an "you guys stole my idea"... (Not that people in the gaming industry would ever steal ideas, really... ), or because someone else wants to ste... uhm... borrow some ideas from ESO, and possibly use them in ways the powers that be would not exactly approve of... well... and perhaps most of all, so they can always use something like a nifty looking character outfit you assembled or player videos of gameplay for their own promotional stuff without having to pay someone if the need should arise...

In the end, I expect it won't really affect us mere players.