Bitcoin can be for retirement. Because when you are already retired and you don't have enough strength on traveling or in doing hard jobs bitcoin is essential to be do. Because in gaining bitcoin you don't need so much effort all you have needed is a personal computer and internet connection and your brain.
I think that the people that hold onto Bitcoin for retirement are relying on it too much. The reason why Bitcoin should not be a source for a reliable income is because the price of it could drop to zero without much effort from someone that decided to purchase a bunch of coins. If a dump like that happened then it would be a while till Bitcoin Exchanges get the money to recover the price.