Well, control add-ins are not new in NAV 2016, they have been around for a long time now. But, they have been improved and this blog post is about these improvements.
Of course, the improvements are exclusively in the Web client framework, not the Windows client, and I am educated-guessing here that we won’t really see many improvements in the control add-in framework for Windows in the future. Why would we? All control add-ins should target all clients and use the Web framework, anyway so the case for Windows client is getting weaker and weaker.