Just a few comments on the code itself:

    if type_ in self.__dispatch.keys():
should be:
    if type_ in self.__dispatch:

Previously, error reporting of recursive data stated the type of the offending value; with this patch, this hint is lost (see _add_memo)

Caching of bound methods in local variables is a common optimization (dump=self._dump); why did you remove it everywhere?

Why Marshaller.dispatch was renamed to __dispatch but Unmarshaller.dispatch stays the same? (btw, why the double underscore?)