In-Game voice would be huge. Pugging in groups of silent non vent users is a pain. i think it would add a bit to the community.

Guild alliance tab w/an alliance chat channel. Which leads me to the next no brainer. RVR. faction alliance V faction alliance sieges.

Capes w/guild emblems.

The economy is very soft. We get so many good items from Planarite or pvp favor that player made stuff isn't very important. I don't have an answer but I'm just addressing a problem. Games w/solid player controlled economies add a ton.