Is it possible to open an ".xfdoc.xlBook" directly through the excel add in? It shows the file within the file explorer but will not let me open. I can open .xls or other shared files, but it doesn't let me open a book? The report book does render fine through the client (it pushes it to excel). However, I would like my end users to just grab the xlbook through the add in versus having to go through the client.
This is currently not possible, sadly. If you look at the File Explorer in the Client, when you right-click on a book, it says "Process and Open" - the server has to do some work on the book before it can be pushed to Excel. Even from the built-in Spreadsheet page, if you try to Open -> From XF FileSystem, you cannot select a book (notice they are greyed out).
You can contact Support and ask them to file it as a feature request. Sorry!