//
// Assembly My.Service1_0.dll
//

interface IService1_0
{
   void Foo();
}

class Service1_0 : IService1_0
{
   public virtual void Foo() { print "Version 1.0"; }
}

class Service : Service1_0
{

}

//
// Assembly My.Service2_0.dll
//
interface IService2_0 : IService1_0
{
  void Bar();
}

class Service2_0 : Service1_0, IService2_0
{
   override void Foo() { print "Improved version 2.0"; }
   void Bar();
}

class Service: Service2_0
{

}

Service service = Activator.CreateInstance(typeof(Service));
bool version1_0 = (service as IService1_0) != null;
bool version2_0 = (service as IService2_0) != null;

    // общая сборка с описаниями типов
    [AttributeUsage(AttributeTargets.Class)]
    public class PluginInfoAttribute : Attribute
    {
        public string Name { get; set; }
        public string DisplayName { get; set; }
        public string Description { get; set; }
        public bool SupportsFeature1 { get; set; }
        public bool SupportsFeature2 { get; set; }
        public bool SupportsFeature3 { get; set; }
    }

    // сборка конкретного плагина    
    [PluginInfo(Name = ...)]
    public class Plugin : IPlugin
    {...}

А>    // общая сборка с описаниями типов
А>    [AttributeUsage(AttributeTargets.Class)]
А>    public class PluginInfoAttribute : Attribute
А>    {
А>        public string Name { get; set; }
А>        public string DisplayName { get; set; }
А>        public string Description { get; set; }
А>        public bool SupportsFeature1 { get; set; }
А>        public bool SupportsFeature2 { get; set; }
А>        public bool SupportsFeature3 { get; set; }
А>    }

А>    // сборка конкретного плагина    
А>    [PluginInfo(Name = ...)]
А>    public class Plugin : IPlugin
А>    {...}
А>

public class Plugin : IPlugin, IPluginDescription
{...}

BorlandIDEServices: IBorlandIDEServices;

IBorlandIDEServices = interface
   ['{C9E8E577-B5D8-43F3-BC84-6A734A015732}']
   function SupportsService(const Service: TGUID): Boolean;
   function GetService(const Service: TGUID): IInterface; overload;
   function GetService(const Service: TGUID; out Svc): Boolean; overload;
end;

public interface IPackage
{
    // Methods
    void Load(IApplicationService applicationService);
    void Unload();
}

public interface IApplicationService : IServiceProvider
{
    // Methods
    void AddService(Type serviceType, object serviceInstance);
    void RegisterPackage(IPackage package);
    void RemoveService(Type serviceType);
    void UnregisterPackage(IPackage package);

    // Properties
    IAddInService AddInService { get; }
    ICommandBarService CommandBarService { get; }
    ICommandLineService CommandLineService { get; }
    ICommandService CommandService { get; }
    IConfigurationService ConfigurationService { get; }
    bool DiagnosticMode { get; }
    IDocumentService DocumentService { get; }
    IErrorService ErrorService { get; }
    IFeedbackService FeedbackService { get; }
    bool IsReleaseVersion { get; }
    ILicenseService LicenseService { get; }
    string LongApplicationName { get; }
    FrameworkElement MainWindowRootElement { get; set; }
    IMessageDisplayService MessageDisplayService { get; }
    IMessageLoggingService MessageLoggingService { get; }
...
}