Why not create both? A 'banter' chat room and also an invite only chat? The invite only would be very useful for cross alliance coordination and the banter chat would clear our common for it's intended use.
I know it may be more work for the devs, but I like the idea of having both, the banter chat and invite only. Now there is much more interaction between alliances, having an invite only chat would be very useful.
Also slightly off topic but a private permanent( at least for a few days) bulletin board for alliance members only, that does not get lost when you log off, would be extremely useful for members to pass on important information to other alliance members.
YES! Loving all these ideas! Especially this last note about having some level of alliance chat that is more visible. That I think is probably the most important... we lose too much info in Alliance chat since we cannot scroll back all the way. And since we're all on different schedules, it would really be beneficial to have that added.
And I definitely love the multi-player invite private chat idea! been thinking about one too for awhile. So glad it's being addressed in this thread =)