Hi, all! I just wanted to quickly warn people looking to use PowerPivot for SharePoint in SharePoint 2016 that there is a bug that they should be aware of. I found it a couple of weeks ago with a customer, and I blogged about it here: http://info.summit7systems.com/blog/bug-report-powerpivot-for-sharepoint-2016-thumbnails-not-generat.... In short, I found that the Excel REST API (which is used to generate Excel workbook thumbnails in SharePoint 2016) has a hard dependency on the localhost URL. If the API is unable to resolve the workbook's locaiton using "localhost" in the URL, then the thumbnail won't generate. You can get it to work for one web application if you configure it just right, but it will be impossible to get thumbnails if you are using additional web applications. So if you're looking to deploy PowerPivot for SharePoint in SharePoint 2016, I highly recommend you review the blog before you get too far committed to your site topology.
For any Microsofties, you may find additional details in case 117021415318755.