We've thought about it, but it's not a very high priority for us right now as it would change our controller caching and invocation systems in a non-trivial manner.  We're playing around with systems that would allow more dynamic selection of controllers and actions beyond what a [ControllerName] attribute could accomplish, but there's nothing yet to report on that front.

There's a workaround for what you wanted:

public class FriendlyNameController : MyReallyReallyLongControllerNameController { }