I really do not know.
The more likely thing is that in 5 years people will say, "what's an mp4?"
I am betting on something like that.  (on that scale)

My personal idea is that the new ThemTube will basically be your browser pulling all the feeds from all that you watch, and what your friends watch... or, something like "your cluster" (people that like similar stuff, like trekies) and then build a trending page on the fly.

Where there really isn't a web page, or central server.