for me the real passive income is saving your money, you save your money now, you can save $100-$500/month then use your saving for passive income in your day of retirement 
The time when you get into your retirement day, the value of your money will be 10 % less atleast. Assuming that the inflation rate is on average of 5 % per year and if you save for 25 years until your retirement day then you could be able to do the calculation of your own on how less valuable your money will be at that time so saving is definitely not your best bet to retire
so should i save my money at bitcoin..? for long time..?, Im trust bitcoin can survive but no body can give you guarantee bitcoin price will be stable at high price (arround $1000). I think save your money for a day or retirement Is best option, we know inflation rate per year is very high but I will save my money in fiat for support my goverment.
and NO body know maybe in future my fiat money can goes up to +200%