OP updated with new artist of the week and news regarding our new 3x Platinum artist 
Great news! We definitely need to have more well-known artists with good listenable music in the MC-ecosystem. Because right now MC is way too indie, if you know what I mean.Yes, I agree.
However I am pretty sure a big artist like Rihanna or Eminem can't just start using MUSIC. They probably got a contract with some music label and aren't allowed to do any business outside the scope of that venue.
Hence the reason why most of the artists are indie because they don't have contracts with any music labels.
And even if an artist did decide to risk it and go with MUSIC, there is very little liquidity right now with the coin. It has a very small market cap and say the artist got 1,000,000 MUSIC every month for their plays, they wouldn't be able to sell it even.