I think that it is actually a realistic expectation that eventually everyone will be using social media of some sort. We're very far from that at this point, but much of that has to do with a disintegration of social media tools with the average person's life.
When my grandma (who doesn't have a computer) is looking at pictures on Flickr because she knows that's the best place to find pictures of her great grandchild, it's not too much of a leap to expect that in 20 years grandparents everywhere will think of using social media tools to communicate with their great grandkids.
That's just one case where social media tools will become integrated into peoples lives; there are tons more that are obvious, others will arise as new tools and systems become available.