Add a tool to delete kafka based consumer offsets for a given group similar to the reset tool. It could look something like this:
kafka-consumer-groups --bootstrap-server localhost:9092 --delete-offsets --group somegroup
The case for this is as follows:
1. Consumer group with id: group1 subscribes to topic1
2. The group is stopped
3. The subscription changed to topic2 but the id is kept as group1
Now the out output of kafka-consumer-groups --describe for the group will show topic1 even though the group is not subscribed to that topic. This is bad for monitoring as it will show lag on topic1.