Where is the difference between right click->exchange symbol and select lets say pmos_GSD or right click exchange mapping and select pmos_GSD? (the right click-> exchange symbol interface will come with v6. This is because v6 will also need right click → update symbol from lib and that one is just a specialization of the former.)
It is the same user interaction, both options need the mapping in the lib somehow (one as part of a symbol that just so happens to inherit the graphical representation of some central entity the other by using a separate file to represent only the mapping)
And the inheritance stuff can even be used to give the user a exchange mapping feature by simply filtering the options of the exchange symbol feature to list only parts that inherit the graphics from the same element.
There is however a catch. Wayne mentioned sometime in the past that inheritance might not get fully implemented in v6. So it might be that the full feature set will only come in v7. (But that does not change with any other suggestion as i would guess that the priority list will stay “get feature parity but with new file format” for v6.)