If you are retiring in 15 years or more its well possible that 1 bitcoin can be enough to retire on even in a first world country. I wouldn't put all my eggs in one basket though and rely solely on that, I would still look at other options just incase.
Bitcoin can be given to people for retirement. Because bitcoin is providing a good service it is increasing day by day and the people who has hard worked in a services like army and nation security related services and so on. If they get 1 bitcoin then it will help them a future. And they will be happy from there life that people are getting the result of there hard work after retirement.