When you're in a clan with a large amount of members, it's difficult to find out who is and who isn't a friendly face in a pvp situation when you don't know everyone.
I think adding client-sided name changes for clan relations would be beneficial so that a player doesn't learn the hard way that someone is their enemy until they're being attacked. This would save a lot of time and stress in a pvp situation so that you're not frantically trying to figure out if someone is on your team or not.
For example, if a player is in your clan, their name would be green; if they're enemied, their name would be red; if they're allied, their name would be blue.
All player names are white, so I personally don't see any issues. Staff do have colored names but it's very easy to see who is and who isn't a staff member.