They might not become mainstream any time soon, if ever, but they aren't going to go anywhere. The concept is here to stay in some form or the other. It's somewhat likely they will become somewhat mainstream sometime soon though given to the fact they are becoming more and more casual user friendly each day.
The only thing that has ever stood the test of time is a commodity that you can hold in your hands. If money is not based on a commodity, there is nothing to limit how much of it is used.
Example: If you could have anything you wanted and pay for it by writing an IOU, you would of course go buy everything you ran across, and your IOU would soon be worthless because everybody had about all the IOUs they could stand. But if you had to eave a tooth with every IOU, then the number of IOUs would be limited by the number of animals and the inconvenience of having to overpower them and yank their teeth, and they would therefore have a specific value.
The only value of Bitcoin is that people can make their own without a government to do it for them. The only value of government issued money is that the government will accept it in payment of taxes. Government money is therefore more valuable than Bitcoin.
