I'm going to add on to this and suggest that all these ingame features could be accessible through the forums, by adding then to the user cp. (ingame ignore list, etc)

Overall, the only problems I see in implementing this, is the abuse that could be summed up by some clever bad guys and the lack of communication in important servers. This, however, is only a minor problem that could probably be solved if something like "user whispered is ignoring you" popped up. I really have no clue why this isn't an option already.