Microsoft indicated in a TechNet article and later tweet (below) that Tags and Notes—among other things—are no longer part of SharePoint starting with SP2016.
— Microsoft SharePoint (@SharePoint) February 4, 2016
Tags and Notes were introduced in SharePoint 2010 as a kind of way to add a mixture of metadata and social functions, but in my opinion they were never really well thought out.
Both were easily replaced by any other text field, so you could get your metadata that way. And the social aspect (because they could be added by anyone, theoretically) was pushing it. They would lead to arbitrary and ad hoc additions of metadata that didn’t follow a taxonomy and were very unlikely to follow any sort of plan. So what value did they truly add?
Apparently not much. Hence this announcement.
So if you were in love with them in SharePoint 2010 and use them, whether in SP2010 or SP2013—they’re not as robustly supported in SP2013, but they still exist—now’s the time to start figuring out how to live without them.