Could just see it as another perk of being a premium member. If they really wanted everyone to know who they are, they'd probably just tell you in their sig etc. If some members just want to change their names and not let everyone know about, then that's there business.
I mean, I really dislike my previous name. Would really be irritating if it were permanently in my profile for everyone to see...
No offense but I really don't think this is a very good reason tbh. What is wrong in other people knowing your old username, no one will change their opinion about him just because of his old username, its just a username. And its not them, but us who would want to know. We may not recognize the username and I think that will be more beneficial and more important than people not wanting others to know about their old username because they are ashamed. My old username sucks too(Federer11), but I wouldn't care if people know about it, its not like people will change their opinion about me because of my old username.
I don't like the idea of forcing it on them by having it in their profile.
But well for the non-premiums, there is a thread about our old usernames so.....
Anyway, if the mods don't like the suggestion then its fine, I can't do anything about it.