The news comes from a post to the Blizzard boards that, like anything involving change, touched off an avalanche of comments from people who make like this is going to be the end of the world. Actually, it's a bit more even than the average announcement, as there are plenty of people piping up in there with "cool" and "wow!" messages, expressing a touch of excitement for the upcoming feature.
It's primarily going in to allow players who leveled up characters on the opposite side as their friends to swap over and join up with their posse. But there aren't really any more details about it out there, so we'll have to wait and see what sort of restrictions are applied and how, exactly, it'll all work.
I suspect Mountain Dew will be involved.