Currently multiprocessing uses the pickle module for its serialization of objects to be communicated between processes.  Specifically v2 of the pickle protocols is now exclusively used to provide maximum compatibility, motivated by the desire for multiple versions of Python to be used simultaneously with multiprocessing.

Per conversations in issue26507, issue23403, and others, multiprocessing should offer the option to specify what serialization is to be used for the transport of data between processes.  Besides supporting requests to use a different version of the pickle protocol or using 3rd party tools like dill, a hook to specify the means for reducing objects to a transmittable form opens a door for other creative or higher performance strategies.

Ultimately, this is not an enhancement to add functionality but rather to reorganize the existing internals of multiprocessing to permit better control over its use of serialization.