The OpenStudio plugin requires users to upload a zip file with an .nbk suffix that contains the notebook .ipynb file and an html export view of it; (the html view can be a bit ropey eg if the notebook has run output cells that originally contained iframes). A crude notebook extension provides a toolbar button to create the .nbk package that uses nbconvert html_embed filter to generate the html.
The original proposal was for an OpenStudio plugin architecture that would allow .ipynb to be uploaded and then rendered back to users of OpenStudio using nbviewer. That was blocked, presumably on grounds of complexity, available project time/resource and maybe also security...