Because you should maintain API compatibility when you tell everyone to use your shit.

fix_requests.py

from requests.models import Response

class fixedjson(object):
    def __init__(self, func):
        self.func = func

    def __get__(self, inst, cls):
        result = self.func(inst)

        class proxy(type(result)):
            def __call__(self):
                return self

        if isinstance(result, (dict, int, float, unicode, str, tuple, list)):
            return proxy(result)
        elif result is None:
            return proxy()
        else:
            raise NotImplementedError

        return proxy

Response.json = fixedjson(Response.json)


import requests
x = requests.get('http://httpbin.org/ip')
print repr(x.json)
print repr(x.json())

Because you should maintain API compatibility when you tell everyone to use your shit.

That's true until major version numbers change. The better option is to update your dependencies such that only versions within the same major version are acceptable. Doing so requires a little bit of forethought, but you should be thinking about that anyway when you "tell everyone to use your shit".

Out of curiosity, not nitpicking, isn't line 21 unreachable?