Hm – I don’t know. Facebook is such a hit I doubt it will meet its end anytime soon, since challengers such as Google Plus have mostly been met with skepticism as far as I know. The beginning of a slight decline, perhaps, as people begin to realise what Facebook gives and takes from them and don’t find it as fresh, but I doubt it will be the end.
In response to the ‘more focused sites will draw people away from Facebook’ comment, I believe that being able to have many ‘friends’ is one of the advantages of Facebook because you can keep in touch with lots of people at the same time, in the same place. And Facebook has already added a Top Friends (or something) feed in addition to the normal News Feed that displays updates from a select group of friends chosen by the user.
Ah well, as said in the article, with technology, you never know eh? 😉