Github user GJL commented on the issue:
https://github.com/apache/flink/pull/5334
I have a usability concern.
It's possible to run
```
FLINK_MODE=flip6 bin/start-cluster.sh
```
This will start a cluster in flilp6 mode.
However,
```
FLINK_MODE=flip6 bin/flink list
```
won't work.
If the first way is not intended, then it doesn't matter.---
