NOTE: The following diagram is NOT a representation of the stack of Release Candidate(RC) version. But it is something which is currently in development and most probably would be available for the final release. If you would like to look at the diagram representing the stack of RC version, you can go here.
A notable difference between the following currently in development diagram and the RC version stack is the addition of a nice feature: Ability for having route-specific message handler pipelines.
Henrik provides a nice overview of this feature over here.
(click the image to get a larger image)