They likely will be dead before Bitcoin goes mainstream. I am only half kidding. Bitcoin is so small that even with rapid growth it could take a decade or two before it becomes as common place as say twitter.
I'm more optimistic. I believe the great financial motivation that Bitcoin provides to early adopters will motivate them to kickstart its infrastructure and applications in a much more rapid way than twitter.
Suppose you're the 100th Twitter user ever. You may or may not have an idea of its vision, but even if you do, it doesn't offer you a great benefit right now because ... well ... none of your friends are using it yet.
If you're the 100th Bitcoin user, and you understand it, then you understand why it's so much better than what was before Bitcoin, and (IMO) believe it will be very popular in say 20-30 years. So you become an early adopter, hoard some coins, talk about it, encourage your friends & family to join...
Bitcoin users have some (maybe huge) benefit from it even before it reaches mass adoption, unlike Twitter.
I think that this Early Adopter Motivation factor can bring about a massive Bitcoin adoption within five years (give or take).
True, there is a lot of existing infrastructure and competition to replace that won't just die without a fight, and legislation will be a bitch. But I'm an optimistic kind of guy.
We'll just have to wait and see.