So, forgive me if I am being insane here, but as I understand it you can currently group and adventure with players from other servers as long as you do so in an overflow.
If you were to enter a map that was not currently in an overflow state, the group would split due to a lack of the guesting feature being in place. They would go to their home world and you to yours.
I was curious to know if it would be possible, as a temporary stop-gap until guesting is added, for every zone to have a minimum of 1 overflow running whether it was needed or not.