I think username changes could be used with coins. I know you can email support and get it changed but sometimes I feel like it might end up in spam or something causing it to never gt resolved unless they email again or make a support ticket.
This way, as long as a person has enough coins, they can change their username as often as they want (or at least once a year or something) like with their display names.
I know the whole thing of broken links but that would be the user's responsibility in knowing that if they change their screen name, their old screen-links won't work.