[MetadataAttribute]
public class Plugin : InheritedExport
{
  public Plugin() :
    base(typeof(IPlugin))
  {
  }

  public string Category {get;set;}
  public string Name {get;set;]
}

[Plugin] //exports IPlugin
public class BasePart : IPlugin {
}

[Plugin(Category="SomeCategory", Name="DerivedPart"]
public class DerivedPart : BasePart {
}