It doesn’t sound bad but understand the volatility of Bitcoin. Also, I think it depends on when you start the retirement plan. If you start from an early age to put those savings in Bitcoin rather than the bank, first, your funds are completely yours, second, you can make some extra if Bitcoin price goes up. Continuously saving more and more over the years would be a good idea because Bitcoin has a trend of good growth. So even before the retirement, the savings could be doubled.