I have downloaded Preview 2, added a reference to System.ComponentModel.Composition.Codeplex.dll from the bin directory of the download.
Add a using statement to System.ComponentModel.Composition...all seems ok.
Perform a build and get the above error...
Error 20 The type or namespace name 'Composition' does not exist in the namespace 'System.ComponentModel' (are you missing an assembly reference?)
and a red squiggly under Composition on the above using statement and the only avail option in intellisence is ComponentModel.Design