SublimeAutoPep8 plugin uses autopep8 module to format code.
I guess autopep8 doesn't do this because renaming functions and classes is rather refactoring than formatting and it's too dangerous.
Anyway, you can ask autopep8 authors about this feature.
like mentioned in https://www.python.org/dev/peps/pep-0008/#function-names , the package doesn't take care of that?