A node that combines multiple Shaders. Would have multiple transfer modes to achieve different looks.
Opened for voting.
Until this feature is implemented, you could achieve the effect of applying multiple shaders to a 3D object by rendering multiple copies of the object, each with a different shader. You’d need to offset each copy a slightly different amount away from the camera to avoid artifacts from inexact floating-point calculations (“z-fighting”). You could use the Change 3D Object Blending node to change how the shaders are composited.
This feature would conveniently wrap the functionality into a single node.