Default for conversion to Word should be .docx

All users would benefit. Almost all WP users need to convert files back and forth to Word format in order to share documents with non-WP colleagues. Currently the default conversion is to the antiquated .doc format. One has to go through extra steps to convert to .docx. .docx has been the standard since 2007--please update the default conversion, or at least give users the option to set what the default is through preferences. Thank you.