Back then, there was room in the world for Facebook to dig its own decently sized moat before it had to meet AOL head to head. Nowadays, that’s harder, certainly in the West.

Because of that, I think it’s likely that, if a company manages to dethrone Facebook, it will come from China, where the government is willing to act as a kind of incubator.

So, IMO, rather than seeing Facebook dethroned, the more likely outcome is a world with two (or maybe three? Europe seems not concerned about being part of the Facebook camp ?yet?, but it, Russia or Arab countries may at some time start helping a large local competitor emerge) giants that split the world geographically, and can’t merge because countries will forbid them from doing that.

I don't know much about the Arab countries, but Russia is perfectly happy with its own state-approved versions of Facebook (Vkontakte and Odnoklassniki).