I've been using the desktop versions of OneNote for many years. My job involves attending many meetings, workshops, conferences, etc, all represented as meetings in my Outlook calendar on my organizations's Exchange server. Most of these meetings are linked to a note in Onenote where I can prepare material in advance, make notes during and after the meeting, insert copies of slides etc. So I can still go to a meeting I attended 10 years ago in Outlook, press the OneNote button and be taken directly to the notes. Conversely, I can go directly to the calendar item from the notes of the meeting. But the links back to Outlook no longer work in OneNote for Windows 10 and I cannot get the Insert meeting details to work for a new meeting.
It was wonderful that these links continued to work even when you move the notes to different sections or even different notebooks. A really powerful, robust and useful feature.
So it looks as if this huge resource of information, going back over many years of my career, is going to be lost when I can no longer use OneNote 2016.
Does Microsoft realise what a disaster this will be?