thank you very much for sharing the design doc. It's very well written document, thank you for doing that! I do have one comment.
The connector will provide one extra argument option -
I'm not sure that this a good idea. Some of the arguments might break the behavior and I'm not sure that users should have this kind of power. I would much more prefer to see each option that make sense exposed as an extra option that we can verify for correctness prior passing to the underlying create external table statement.