As discussed in
SPARK-2420, this task covers the work of shading Guava in Spark deliverables so that they don't conflict with the Hadoop classpath (nor user's classpath).
Since one Guava class is exposed through Spark's API, that class will be forked from 14.0.1 (current version used by Spark) and excluded from any shading.
The end result is that Spark's Guava won't be exposed to users anymore. This has the side-effect of effectively downgrading to version 11 (the one used by Hadoop) for those that do not explicitly depend on / package Guava with their apps.