Hi Eric, the REST api to upload a .pbix file is described at https://msdn.microsoft.com/en-us/library/mt243840.aspx. This creates a new dataset in your cloud account and creates reports based on what's in your .pbix file. I've done this successfully.
However if then you want to manipulate this data with some of the REST apis like a Row Operation (https://msdn.microsoft.com/en-us/library/mt203566.aspx), those operations will fail. At this time, it doesn't appear that you can manipulate the row data from a .pbix that you uploaded.
The only way that you can do direct push of data is to create the tables and schema yourself and then send the data. Alternately there's a new way in the web client to create a real-time data source. But, the point is that the data is in the web client through either of these methods, and it seems you have to author reports there. I don't see a way to author offline in the desktop client and then match that up with real-time or push data once you've sent your report definitions to the cloud.
Chris