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.
I know that prices will be high in the future. But 1 btc for your retirement, I think it will be very less .. because of you after you retired. There probably will not be any big earnings coming in. So you have to prepare a lot of money for your old age
Even if a bitcoin reaches $10,000 in the future, I doubt if that would be enough to really cover all the expenses on a daily basis, especially when you are retired and doesn't have other means of income. Better still to diversify and save as much today so that you could live a more stable, worry-free, comfortable life in your retirement years, be it on a first or third world country.