The idea is great however a company like Soundcloud would rather have full control than rely on a third party as there are just too many risks.
If this was an avenue they were to consider then they would either buy out someone like musicoin or hire developers to do this themselves.
I have been using both sites for sometime and I am very excited about the future for independent artists with sites that utilise the blockchain but musicoin has long way to go to become a proven technology. At the moment it has a lot of issues in terms of performance and scalability and this would also be a real worry for Soundcloud.
I'm hoping that these performance issues are being worked on behind the scenes and we will see a great improvement soon.
One thing that could happen, if they do get this right, is that a lot of musicians will move over to musicoin from Soundcloud. Who wouldn't want to get paid for every play>?