In a not-so-surprising move, Microsoft is trying to streamline the number of different versions of OneNote it supports.
As of later this year, when Office 2019 launches, Microsoft will be replacing OneNote 2016 with the Universal Windows Platform (UWP)/mobile version, known as OneNote for Windows 10, for both Office 365 and Office 2019. Microsoft will continue to patch and deliver security updates for OneNote 2016 until October 2020, but it isn't adding new features to that desktop version of OneNote.
Update: It turns out Microsoft is not dropping support for OneNote 2016 in 2020, after all, even though Microsoft's original blog post said it would be supported for only two more years. This Frequently Asked Questions page notes that Microsoft will continue to offer security fixes for free for OneNote 2016 under Extended Support until October 14, 2025. Office 2019 and Office 365 users will be able to continue to use OneNote 2016 alongside the UWP Windows 10 OneNote version.
Also: 7 ways you can (maybe) get Microsoft Office 365 for free
Why is Microsoft going with the less-fully-featured version of OneNote, even in its local Office 2019 version of its suite? Here's the company's official rationale in its April 18 blog post about the coming change:
Why OneNote for Windows 10? The app has improved performance and reliability, and it's powered by a brand new sync engine (which we're also bringing to web, Mac, iOS, and Android). You don't need to worry about being on the latest version since it's always up-to-date via the Microsoft Store, and it lets us deliver updates faster than ever before.
Microsoft officials say they've added more than 100 OneNote 2016 features to OneNote for Windows 10 in the past year and a half, at customer request. Microsoft is going to add a few more OneNote 2016 features to OneNote for Windows 10 "later this summer," including the ability to insert and search for tags; see live previews of Office files; and support for Class Notebooks.
There are also a number of features in the OneNote for Windows 10 version that are not in the OneNote 2016 version of the product, such as ink effects, improved ink-to-text, Researcher, a notification center and more, officials stressed.
For a list of some of the features that currently are available in OneNote 2016 vs. OneNote for Windows 10, check out this Microsoft blog post from March this year.
At Ignite, Microsoft announced Office 2019 would be available in calendar 2018, with a preview coming by mid-year. Earlier this year, Microsoft reiterated that plan, officially stating Office 2019 will ship in the second half of calendar 2018, with previews of the new client apps (Word, Excel, PowerPoint, Outlook and Skype for Business) and servers (Exchange, SharePoint, Skype for Business) coming in the second quarter of this year.
Microsoft officials also have said that they'll support Office 2019 on Windows 10 -- not on Windows 7 or 8.1.