Python makes the contents of the docstrings available as a __doc__ attribute attached to the function/class/variable object.
So, you could trivially write a Python program which converts the documentation from whatever format you like into whatever format you like. You could even use Javadoc styling, or XML, or whatever.
Incidentally, since Sphinx is written in Python, making it take non-RST input is just a matter of writing a small amount of Python code.
