Well we're at 4 or 4.5 now.
1. YouTube
1.5 YT Music (basically a music-oriented front-end to YouTube)
2. Google Play Music All-Access
3. YouTube Music Premium (from the article)
4. (or 3.5) VEVO
I particularly enjoyed this quote:
> The days of jumping back and forth between multiple music apps and YouTube are over.
As the above list shows, this is demonstrably false. Given that YouTube Red (or YouTube Premium as they'll soon be rebranding it as) is also part of this package, Google Play Music All-Access is beginning to resemble something of an AV-oriented Prime membership. Lots of benefits, not a lot of focus, but hey, maybe they'll buy up PornHub and add PornHub subscriptions to the stack whether you want it or not, just to make your recurring monthly payments a bit stickier.