My answer to technical support:
Hello Andrew
Thanks for your answer. I understand your argument:
“The Prolog/Epilog options are essentially there to specify the order of shapes appearing in a graphic.”
OK. But from my point of view they should be more general: Enhance a graphics with some more graphics. In our case: Enhance some 3D-Plot (or -Chart or the like) with any standard Graphics primitives, and - of course – even 3D primitives. This can currently not be done. (It can be reached with Show or Overlay, but not directly within the 3D-Plot).
For me the sequencing done by Prolog or Epilog does not mean behind or before in space, but drawn before or after (with respect to time) the main 3D-Plot.
“If you specify Prolog in a 3D graphic, you are stating that the object will always appear behind every other graphic; because of that, only 2 dimensions are needed.“
From your point of view this is true since you allow only 2D Prolog/Epilog. From my point of view including 3D Prolog/Epilog, it is not true.
A small Example: You draw some 3D surface with Plot3D and then you want to mark the maxima by a Point, an Arrow and some text (or a Callout). Currently you cannot do that within Plot3D. (Well you could misuse LabelingFunction in some tricky (If {x,y,z} nearest to a maximum, …]) way for that).
I think the restriction to 2D-Prolog/Epilog is far too strict. And I suppose, allowing for 3D as well would be very consistent with the Wolfram graphic language and would not be very difficult for you to implement.
Kind regards
Werner Geiger