First, DI is a run-time composition concern, not a run-time configuration concern. While the XML support offered by most frameworks could be used to facilitate general purpose plug-in support for an application, the ability for an end-user to change every dependency within an application is generally not needed and even undesirable. Additionally, the configuration schema of most frameworks isn’t designed and optimized around extensibility (i.e. it isn’t designed to make end user configuration simple and straight forward).

Second, XML-based DI configuration offers no intellisense. This means the configuration is not as discoverable, will be more tedious to setup, and delays the discovery of configuration errors until run-time.

Ultimately, DI is really a necessary evil required to accommodate loose coupling within an application. If you are looking for plug-in support, I would recommend examining the Plugin pattern or exploring MAF and MEF.

public static IUnityContainer RegisterType(this IUnityContainer container, FactoryDelegate factoryMethod)
{
container.Configure().RegisterFactory(factoryMethod);
return container;
}

public static IUnityContainer RegisterType(this IUnityContainer container, FactoryDelegate factoryMethod,
LifetimeManager lifetimeManager)
{
container.RegisterType(lifetimeManager).Configure().RegisterFactory(factoryMethod);
return container;
}