Antoine beat me to it and he is totally right.

Please don't derail this bug report. I agree with your analysis that the RNG core of random.Random subclass can't be replaced easily and that more implementations for different purposes would be great. You should stick the analysis into a different ticket or write a PEP. This ticket is the wrong place. I'll support you if you keep the ticket on course. ;)

Let's concentrate on the topic at hand and discuss if 

a) my patch handles the fork() issue correctly
b) if it's a good idea to try SystemRandom first
c) a backport to 2.6, 2.7, 3.1 and 3.2 is required
and perhaps
d) if I should open another ticket to work on a general solution for the RNG + fork() issue.