Just came here to post the same as a new feature request, but then I found yours. I wholeheartedly support it 
Use case: Sometimes, I need to save markdown that others need to view without rendering (e.g. via terminal). In such cases, auto-formatted tables would come in very handy.
I tried using the WYSIWYG-editor as a "formatter" (make slight change to table in WYSIWYG to see if it looks nicer in markdown afterwards), but got rather the opposite from what I hoped for:
Before (table manually written in markdown)
After (using the WYSIWYG-editor to add a row)
