When you open office 2013 and click "Open", you have 3 choices by default (Recent, OneDrive and Computer) and the possibility to "Add a Place".
I would like to create a add-in to add a custom place...
See, I develop a Electronic Document Manager software, and I provide a add-in to office suit, this would be another feature of the add-in.
Instead of "saving-locally-and-uploading-the-file-to-the-site" and/or "downloading-document-and-read", the user would just open and/or save to the site... I would use the Save/Open event to check if everything is right and the user has access and etc...