In addition to the Exchange Server 2016 book, a series of books are being written to further our reach into other audiences. These books will be for other engineers who may not manage Exchange, but instead work with Azure, Skype, Active Directory or SharePoint. These books will be written with or by other authors.
The below list is not comprehensive as not all projects are started or authors chosen:
Other potential titles:
Windows 2016 Active Directory
Skype and Skype Online