The document says "Your app can use the Windows file picker by using the Windows.Storage.Pickers namespace for opening and saving files to the user's OneDrive. " When FileOpenPicker opens the selection window, OneDrive is nowhere to be found. The app has signed in with scope "wl.skydrive_update". Could anyone offer a tip on this?
Are you using a Windows 10 Universal App? As far as I know this is not supported on Windows 8.1.
Edit: (after testing I know Peter is right) This is an amazing feature that I never knew existed. As Peter explained, I just tested it and using the pickers you can open existing files in Onedrive and also create new files in a Windows 8.1 store app.
This may not work as well in Windows 10 because I believe they are changing Onedrive to only show the files that are "selected" for syncing and you won't see all the existing files by default. Maybe Peter can comment on this.