Just a passing thought...
After reading the above, it seems to me that posting covers on Youtube and then Youtube monetizes them for the copyright owner is pretty much equivalent to the old days where if I liked a song, I'd go and buy the sheet music.
In both cases the original copyright owner gains. I suspect that monetizing on Youtube would be a whole heap more beneficial to the original copyright owner than the sale of sheet music.
When I consider Joanne Cooper's site with its 21,000,000 views, I'm pretty sure that that's a big enough number for Joanne to be respected as a 'good financial opportunity' for the original owners of the songs that she posts. It's definitely a win-win situation.