This isn't exactly what writers wanted. They were hoping to be paid per stream, which would give them a direct stake in the success of a popular tune. However, the National Music Publishers Association's David Israelite called it the "best songwriters have ever had" under the current compulsory license system.
There's no guarantee this will make writers happy. Musicians frequently complain about low royalties from streaming services, and songwriters frequently get the short end of the stick even in those conditions. It also raises questions about how the streaming companies themselves will account for this pay raise. They may not have to increase your subscription rate to make up for the difference, but that could mean having to accept thinner profits to get your business. Mind you, this could help everyone involved if it convinces more artists to stream their music.