A few ideas that seem to be common practice in low pop. servers, they've probably been discussed before but here they are again anyway ^^
1) Cross-faction world chat - Both Alliance and Horde players able to communicate through World Chat or other /join <name> channels, and able to add each other as friends. (This may already be possible, but i'm yet to witness it as i'm pretty new)
2) Cross-faction party - Dungeon groups become twice as likely to encounter, being one of three reasons to play WoW: PvP or PvE or Socializing
3) Cross-faction GM/Volunteer guild - If it's possible to do this for only one particular guild, then it'd be fun if new players had somewhere to go before flying the nest and creating their own guilds :)
4) Automated messages to all players informing them about the World channel, recent updates, where to post their bug findings, or friendly messages of the day to keep them informed and give them a "Live" atmosphere
5) PvP zone where players can teleport to, to duel, discuss PvP or go to meet others, it may be against the Blizzlike experience but it'd be cool to have somewhere to "check if anyone's on" sort of thing. Maybe with some location specific misc. items and a buff NPC for fun/enhancing buffs that would only work in that area (It may be too complicated, I have no idea how difficult these things are to setup, but a PvP chill zone could be a sole reason for someone to play on this server too).
6) Making WSG available for a minimum of 2 players (1 from each faction) Win-trading is possible in other ways too, so a permanent ban should solve anyone abusing that.
7) Refer-a-friend system that could give you and your referred friend a welcome/thank you package after reaching 12 hours played, possibly.