Currently stretch database in SQL Server 2016 moves the entire table to Azure. However, this InfoQ article mentions an "archive row" mode for Stretch database that will allow you to filter which rows in a table to move to the cloud (ex. records before 2010). I haven't been able to find any official Microsoft documentation regarding this unreleased feature.
Can someone point me to an official source that says this is coming for RTM? I did find a French blog entry on MSDN mentioning it but nothing else.