The big point of this move is the hit it will have on on-premises Hadoop offerings: Cloudera, Hortonworks, MapR. It's a massive vote of no-confidence in their offerings.
Spotify are effectively ditching a 2000 server, 90 PB Hadoop cluster to go GCE. As Spotify say themselves, that's big news....
Spotifier here. This is an important point. I have nothing bad to say about Cloudera or HWX (disclaimer: we're an HWX customer - we've had a pretty good experience), but I don't really see a compelling reason at this stage to manage your own cluster(s) (HIPAA/regulatory constraints, maybe?)
Getting shared-storage and indepedently operated/scaled compute clusters on top of that storage isn't easily achievable with the standard Hadoop stack, and building that on top of HDFS is non-trivial.
In fact, I don't think large orgs like you (Spotify) really want independently operated clusters. That prevents easy sharing of data, causing data silos to appear. You really want to have true multi-tenancy, which isn't in Hadoop yet. Hadoop has worked more on Kerberos support at the cost of features like easy-to-use access control - Apache Ranger or Sentry anybody!?!?
