It must be brought up and shoved down the gullets of the people as often as need be, until a sufficient change has been made. Like the U.S. Congress
On a serious note, I would be in favor of this as an extension, but not at the core. I say leave the choice up to the Administrators. Someone can write up an extension that would add nofollow tags to posts, signatures and profiles, with conditions for each set in the ACP.