Another tab like the "Guild Roster" but with at least with the Guild Leader and Officers of all allied guilds. A +/- option for each guild would help keep the size down. It would make it easier to "whisper directly" to someone without having to fill the friends list with alliance members, or broadcasting "Is ...... of [....] online right now?".
Sorry if anyone else has made this suggestion (making this a double post) but this idea has eaten at me for months and I finally decided to post it.
Prepare for the flame fest from other users lol