I've tried this twice, unfortunately the first time I seem to have lost some real data (though perhaps if I'm lucky and it's a fixable bug I can get it back):
If I create a new Notebook, choose OneNote format, then create some pages. I can add data to those pages and all seems fine as long as the Outline app keeps running. Once I close the app though and come back in, all the pages that I created are completely blank and can't even be edited. They are weirdly just a white untouchable page.
This is just being written to local Mac disk.
I have OneNote notebooks that I opened, imported, and saved of from ".onepkg" files in OneNote format, and those edit and work fine.
I am running the latest and greatest Sierra with all patches to date.