Someone recently asked under which circumstances SQL Server 2014 would return false when interrogated for the IsXTPSupported server property.
I looked into the source code and this is what I encountered there. For the boxed version of SQL14, that server property would return FALSE if:
1) lightweight pooling (fiber mode) is enabled,
2) the instance is not one of the SKUs where the feature is supported (Enterprise, Developer, or Evaluation), or
3) the PF_COMPARE_EXCHANGE128 processor feature is not supported by the computer where SQL Server is running.