The difficulty bomb will make it so the number of coins needed to pay the artists per play, even at fractions, will not even be close to enough. Keep in mind that as more people use Musicoin, more coins are needed to pay artists. The 'plays' are not free, they are paid from mined blocks on the Musicoin blockchain. When the # of coins created drastically drops by 90+% overnight, that business model no longer can sustain without generating revenue through the site to supplement the 'free' plays.
The current model will get decimated by the difficulty bomb. Not many people understand this.