SQL-DBA-01 (7/2/2015)
It says : "Stretch Database lets you archive your historical data transparently and securely. In SQL Server 2016 Community Technology Preview 2 (CTP2), Stretch Database stores your historical data in the Microsoft Azure cloud. After you enable Stretch Database, it silently migrates your historical data to an Azure SQL Database."It has mentioned about migration, so how the point which is mentioned as "extend to addition" fit, I don't know.
I thought it was an extension of your on-premise database to the cloud, so you can store whatever you want there. I've only seen a single presentation on it and haven't installed it, do my knowledge is pretty limited, but that's the impression I have.