I don't know of anyone.
I have been connecting Tableau 8.3 to SAP BW, and to me BEX queries are the best option to connect and work with.
Although you will have limitation related to BEX query that it should not contain any run time variables to be passed. All variables needs to be converted to static value before using it in tableau.
This issue related to variables in query is been taken care of in version 9.1, but i haven't tested it yet.
I heard about the BEX workbook in the Tableau Conference this year. Do you have any experience with BEX workbooks? I was thinking it might be a good alternative around the SAP extract limitation.
Just wanted to get your thoughts and ideas if you have experience with BEX workbooks if they are cleaner to work with and have no missing data?
I would appreciate your feedback,