It would be nice if I could connect to data sources on multiple instances of Tableau Server (or even multiple Sites).  Among other things, this would make it easier to publish a workbook from one Tableau Server instance that connects to a data source on that instance to another Tableau Server instance with a copy of that same data source.  Right now I have to download the workbook and a copy of the data source and save them, then close Desktop and re-open them, log on to the new Tableau Server instance, replace the data source with the one from the new instance, and then publish the workbook up.