Moore's Law has not been improving batteries, which is the real problem. Mobile P2P nodes need to be awake most/all the time, which is a real battery killer. Modern devices have improved battery life by being asleep almost all the time.
Depends on what those p2p nodes are doing. We do p2p on mobile but it's to allow the mobile device to act as a client to access an IoT device, not to force the mobile device to act as a CDN node. Spotify was doing the latter, which is more problematic.
Moore's Law eventually will matter, since faster and more efficient chips equal the ability to do more with lower power consumption. Batteries aren't getting better fast enough, but power consumption per fixed unit of compute is falling like a rock. As a result "effective battery life" for a given fixed workload is subject to Moore's Law.
Regardless of why Spotify phased it out, I think peer-to-peer is fundamentally the wrong way to deliver that kind of paid service. If I'm paying Spotify for the service, then Spotify should bear the cost of delivering it. Not me, and not other customers, in the form of increased bandwidth and power consumption.
Fewer than a quarter of Spotify users are paid users. The P2P model makes a lot of sense for a data-rich service like streaming music, where most of your users do not pay anything.
[0]http://www.csc.kth.se/~gkreitz/spotify-p2p10/spotify-p2p10.p...