A Google SEO themed parody of Blank Space by Taylor Swift that I saw on Twitter led me down a rabbit hole of Black Space covers. People are getting millions of views doing this stuff. Maybe I should practice the ukulele more often. I didn't find a metal version of the song - so maybe there is an opportunity there for somebody.
More seriously though, I have to think 11 million views on a YouTube video adds up to a pretty decent chuck of change. On googling around I found mostly speculation and little actual fact. Technically all these videos need a minimum of two licenses (mechanical and sync), although I suspect most didn't bother. YouTube allegedly makes about $8000 in ad revenue for 1 million videos viewed. The Bieber wannabe with 11 million views, assuming he gets 1/3 of the ad revenue, could have made over $25K.
Given the views here, this is not a hobby that somebody can make a buck at. Posting cover tunes on YouTube is big enough to qualify as a business. Not too shabby for a creative outlet that didn't even exist 10 years ago.