I just got a copy of the Office 2016 public preview today and started OneNote 2016. One of the things I noticed was how little has changed about the desktop version between 2013 and 2016 (too bad). The next thing I was curious about was whether or not the Onetastic add-on would work with the new preview version. As it turns out, in fact it works perfectly!
The Onetastic plugin in OneNote 2016 Preview
Additionally, the OneCalendar plugin seems to work as well (though it did seem to get stuck on the “Choose a language” page, and I had to close it and reopen it before it opened properly).