I suppose this was inevitable, but if Microsoft doesn't add features such as unread indicators and activity notifications that work with notebooks shared on OneDrive for Business or SharePoint to the cross-platform version of OneNote, it'll be time for me to consider making Evernote my primary note-centric content/collaboration app again. See this Microsoft post for more details on the end of OneNote 2016 and what's coming in the cross-platform OneNote app.
"Microsoft is planning to launch Office 2019 later this year, and the company is changing the way OneNote is bundled. The note taking app currently has a desktop version included in Office 2016, and a separate Universal Windows App for Windows 10. Microsoft is replacing the desktop version of OneNote with the Windows 10 version in Office 2019, along with making the entire Office suite only work on Windows 10. Microsoft is also creating a Mac version of Office 2019.Microsoft Office 2019 kills off OneNote desktop app in favor of Windows 10 version - The Verge
The existing desktop app, OneNote 2016, will no longer get new features but Microsoft will keep updating it to fix any security issues or bugs until its end of life in October 2020. Microsoft has been gradually improving its OneNote Windows 10 app in recent months, and the company is planning new features in the future. OneNote for Windows 10 will receive updates that include the ability to insert and search for tags, see live previews of Office files within OneNote, and Class Notebook features this summer."