I just tested on SQL Server 2012 and 2014 and nulls first/last is still not supported.

The issue you mentioned is closed as "Won't fix":
https://connect.microsoft.com/SQLServer/feedback/details/329337/nulls-ordering-nulls-first-nulls-last-sql-2012

I've confirmed that your fix for SQLServer2008Dialect does work for SQL Server 2012 and 2014 though.