In 10 years of baking head/character displacement maps in production in Zbrush I have never once used the Cage feature. The Cage feature in Zbrush is identical to the Apply Base feature in Blender. Why not just fully automate the propagation from high to low subdiv levels and get rid of this Apply Base button? To me it seems redundant. Nobody in production is going to be deriving displacement maps from a base mesh that is so radically different in volume/form from the Cage mesh.