Yes, we already have the option to show new and departing players, but that always clutters up my chat window with a bajillion other people I don't know and don't care about. So I leave those options off.
For a long time now I've thought that some sort of system for showing only specified new players would be great. Maybe we could even do something by faction-tags, so that you're notified when other members of your faction log on.
And if you guys really think that this is so "abusable", then fine, we can have a /acceptfriend and a /declinefriend. But, like TheJarl said, we already have the "new player" option. If someone really wants to know when someone gets online so they can go shoot them, they're probably already using that anyway.