Hi Terry,
You are correct that support for SQL Server 2014 is not available at 10.2.x releases.
Support for SQL 2014 starts with the 10.3 release: SQL Server 2014 for ArcGIS 10.3
As for any serious issues using SQL Server 2014 with ArcGIS 10.2.x or ArcGIS Server there may be some unintended issues that are not documented and may pop up out of the blue and be difficult to resolve, if the environment is not supported. I would recommend waiting to 10.3 final is released before upgrading fully to SQL Server 2014.
Hope this helps....
-George
--- George T.