Knowing when someone has changed their name on your friends list is something I would be very much interested in.
- An icon next to someone's name for 30days indicating they've swapped.
- The previous name listed for 30days in their search info

Anything along these lines.

Please don't include a complete history of name changes.
Some people want to escape their old identities and MMOs by nature are so heavily invested in their social aspect, that if you fall out with someone, you might drop the game completely.