Slack handles this quite well actually. I know a lot of people dislike Slack for a lot of valid reasons, but they handle a few things right. If I type a message on Slack saying "hey, @alice, what's up?" then "@alice" gets replaced with the person's real name "Alice". When I send the message, the "Alice" bit in the resulting message becomes a link that will open the user's profile. Additionally, if "Alice" ever changes her name OR username, the name updates accordingly.