Sharing maps is simple, just copy your map file, upload it to whatever file sharing site you want, and post a link. BAM, done.
As for an in-game sharer? Unlikely. One of the cool bits that a fair number of players like about cataclysm is that it doesn’t connect to the internet and is totally self contained.
As for a map editor that actually works from the overlap, it’s something that could certainly be possible later, but AFAIK there is still quite a bit of weirdness in coordinate stuff between the map and overlap, which makes any sort of editor on that scale more difficult to do.