I would love to see a core OS install running SQL Server. There are still many times when apps on the SQL Server would be necessary likewise there other reasons to not implement a core only model. It really depends how granular of an implementation a person wantseeds.

http://msdn.microsoft.com/en-us/library/ms143506.aspx -- "SQL Server 2008 is not supported on Windows Server 2008 and Windows Server 2008 R2 Server Core installations."

Unfortunately SQL Server 2008 is not compatible with the Windows Server 2008 Core only installation. Maybe it is part of MS long term upgrade strategy.