3 sounds like the RealID system Blizzard put into Warcraft, you could talk to anyone in your RealID list regardless of what faction and server they were on. Quite usefull that was.

It would be a nice feature, though you'd have to have people to talk to on those other servers in the first place.

They could perhaps add it if they fix the party search menu, so instead of just trying to find parties in your area on your server, it looks on all servers, when it finds one, any players just join that party is instanced into that server for the duration of the party, and then moved back upon leaving the party, which would make getting groups for dungeons and stuff better.

A good idea either way, but it'd be pretty tough to impliment.