Hahahahahahahaha!!!!

[headsplice]

The problem with Bobbit-izing a rapist is that rape is not, primarily, about sex. That is the means, but the underlying drive is a power drive.
"I control this person in the most intimate way possible."
They could just as easily use a bar stool leg or a vibrator and get the exact same effect.
A better punishment is for them to have the exact same feeling of loss of power. Obviously, that hasn't been tested, but there are lots of people out there on whom it could be, and that I whole-heartedly endorse.