This has been discussed a few times in the past, but now Oracle has ended support for Java 6 for over a year, I wonder if we should just drop Java 6 support.
There is one outstanding issue Tom has brought to my attention: PySpark on YARN doesn't work well with Java 7/8, but we have an outstanding pull request to fix that. https://issues.apache.org/jira/browse/SPARK-6869 https://issues.apache.org/jira/browse/SPARK-1920
