If a package creator wants to install different assemblies based on, say, the version of Razor used by a project, or of Entity Framework, she wouldn't have a good solution today, short of writing custom code to interrogate file versions is a powershell script, to do so.

See the post at http://nuget.codeplex.com/discussions/428681 for a concrete example of the problem.

We should provide a mechanism -- perhaps expanding our notion of a framework version in our folder structure -- to support this scenario.