You don't need to come up with a new and better email system, you just need to come up with something completely different that is not as flawed and is more user friendly (e.g. Facebook).
The Internet probably will change dramatically. But even if it doesn't, that is quite a bold claim that you can't replace Facebook with a new and better product. The possibilities and innovations are practically endless. For instance, who the heck would have thought Twitter (of all things) would have become so popular? The concept initially seems rather silly.
Sure, someone can replace Facebook. Someone can also come along and replace Microsoft, Exxon Mobil, or ADM. Do you see that happening? No.
The internet will continue to evolve, but there is no reason to think that Facebook won't continue to evolve, too. In the same way nobody saw Facebook as a threat to Google (which it most clearly is), the potential threats to Facebook are companies we haven't even thought of yet, not another social network.
Facebook's defenses against being replaced are far more developed than MySpace or whatever.
First, they have a tremendous userbase. Facebook users uploaded nearly 750 million phoos on NYE alone. They have over 200 million people who log in daily.
Second, they are making themselves more than just a website to chat with friends, they're becoming a social platform. With their games and apps you can now create programs that easily interact with your friends, feed data back into a centralized placed, and be deployed across platforms.
Third, they are integrating themselves into the rest of the internet. By offering Facebook Connect, Beacon, Instant Personalization, and their forthcoming ad platform, Facebook is slowly getting itself integrated into the biggest websites on the internet and by doing so, they're furthering their users' dependence
I have no doubt that Facebook is changing constantly, if it didn't it wouldn't survive. But constantly changing doesn't insure survival 100%. A great many other things are constantly changing as well.
This statement is a fact with any company, big or small.
Facebook got those 1/2 billion users somehow, and by the same process it acquired those users, something else can come along and steal them away.
Sure they can, but they won't. Facebook came into the heyday of social networking. Most of your buddies didn't have social networking accounts and, if they did, they didn't have 4 or 5 years of information sitting in it. That gives Facebook an advantage. On top of that, one killer feature won't be enough to pull people away. The potential "Facebook Killer" is not a Facebook clone. Just like the Google killer was not / is not another traditional search engine.
It's false to say that you would have to convince all 1/2 billion users to switch. In fact, I would say that all it would take is a significant number of relatively popular users to defect to a different site/service. After that, the rest of the sheeple will follow. Why would they do this? Because 'cool' doesn't stay the same thing for very long. I'm sure being on Facebook was very hip and cool in the beginning, but after a certain period of time the cool factor of Facebook will decline. Then, a site will pop up that has some 'wow!' gimmick that allows their users to maximize their narcissism to the degree of Facebook squared. After that, people start jumping ship to get on the hot new thing.
Really. How are you going to convince anyone to switch to a new social network where none of their friends are, none of their data is, all while they have a perfectly good account at Facebook? This will not happen. Period. What will eventually challenge Facebook is something that only vaguely resembles it and certainly doesn't try and clone it.
If the investors at Facebook want to keep their users longer term, they should probably think about cutting their most popular users in on the action (e.g. giving them a small % of the ad revenue generated by their Facebook page). On the flipside, if I were to start a social networking site, I would probably pay celebrities to close down their Facebook pages and start up on my site.
Why? Facebook has over half a billion users, almost all of whom willingly post data and log in every day. There are zero threats to Facebook right now. None. Why the fuck would you start trying to bribe people to stay at a website that they want to be at already AND when there are no alternatives?
As for your "idea" it wouldn't work. Celebs would continue to post on Facebook and Tweet and nobody would visit your site.