First off, I'd like to see some additional proof that this isn't a hoax. There's other people in that thread claiming it's real, but I have yet to see anything other than the image posted.
Assuming it is real however, this is another baffling decision Youtube has made in recent months. I assume the thought behind this is to try maximize their walled garden in some way, but unlike other sites Youtube has such a long history of being embedded in external sites that they can't block all external access all at once. However, the main continued success of Youtube is arguably the emergence of new viral videos that boost new blood into a position of becoming a long-term profitable creator. This is being done in the name of "small creators" but it seems apparent this will have the opposite effect.