Is it possible to get a summary of tomorrow in the Notification Centre with iOS 10?
The "Tomorrow" built-in widget has been removed from iOS 10.

You could use the calendar app Fantastical. It contains a widget which can display a calendar view of the current month, with a list of events for each day, and you can tap around on the calendar to change the day being viewed without ever leaving the widget. It would require an additional tap versus the Tomorrow view, and it's not a summary so much as an actual list, but it's a decent alternative for your use case (and a great app in general, in my opinion).