Initial PySpark-k8s bindings have just been resolved (
SPARK-23984), but the default Python version there is 2. While you can override this by setting it to 3, I think we should have sensible defaults.
Python 3 has been around for ten years and is the clear successor, Python 2 has only 18 months left in terms of support. There isn't a good reason to suggest Python 2 should be used, not in 2018 and not when both versions are supported.