Spamming aside, a set of global chat channels would be a great way to find and organize people interested in exploring the same content in this game. I suspect Content Finder will alleviate some of the need for shouting for parties.

As for why is hasn't been done already... I would guess it's because the servers can't handle sending shouts to potential every player in the game. It's probably the same reason that LS are limited in size. All that chatter being sent to hundreds of people...