As you can see from the below slide, these are the identified issues and limitations that we have with the Stretch database within SQL Server 2016 CTP 3.0 release. A table that has more than 1023 columns or 998 indexes is not eligible to stretch it to Azure. Also the constraints like Check, Foreign Key, Default are also a huge restrictions placed on OLTP schema systems. This Stretch database concept highly works with OLAP based systems and /or if any table that is been isolated without any relations to anyother table. You can also check this article to identify whether any tables within your database is qualified for stretch or not.