Not sure if I'd call it a blocker, but if we can get it in I would *really* like to see some solution to
https://issues.apache.org/jira/browse/KAFKA-2397 committed. Without an explicit leave group, even normal operation of groups can leave some partitions unprocessed for 30-60s at a time under *normal* circumstances like a graceful shutdown/restart. It might be manageable, but that's a pretty large availability gap...
Not that the length of tests is critical, but this is also very obvious in system tests. The copycat tests take about 50% longer than they should because they have to wait for the session timeout.
-Ewen