I can't really see any cryptocurrency being an efficient source of income. The price fluctuates way too much. One day you could have 50,000$ in a certain coin and the next day you're flat broke and can't pay bills. Of course it would work if you were very, very good at predicting the price of the coin so you can exchange when you feel the price way going down, or get more Bitcoin when you think it is going to go up, but you'd already most likely been in luck for a stable job if you were good enough at that. 
There is a method that Cryptocurrency could provide a stable income for someone trading Bitcoins for altcoins.If the price that they exchanged their Bitcoins for altcoin was really low then they could make a bunch of money on some kind of pump that allows their coin to grow past 999.99%. If it's a good coin then that will allow them to cash money out without worrying so much about the price.