For some, the Worgen seem unlikely members of the Alliance. These lupine creatures have a long history within Azeroth, even if no one is quite sure where or - to quote Chris Metzen, "when" - they come from. The choice to include the isolationist zone of Gilneas is logical. After all Arugal's infamous Shadowfang Keep is located just north of the Greymane Wall, right up the road. Added to this the fact a Gilnean hasn't been seen in a decade, well that makes them ripe for a lorefest. Blizzard have all but confirmed it was their isolationist attitude which led to the people of Gilneas becoming Worgen but if that is the case then it's kind of ironic. They hid to escape the undead plague and instead succumbed to another infection entirely.
Formally humans and now Worgen, the trailer hints that it will be the efforts of the Night Elves which will see the Worgen joining the Alliance. Now this in interesting because the Night Elves have their own history with the Worgen, Velinde Starsong and the Scythe of Elune. But given that the Gilnean Worgen are the only other Alliance race who can become Druids, there's an even deeper link between the two races. Also, given that Druids are skilled shapeshifters, the Night Elves could hold the key to helping the people of Gilneas deal with their curse.
Now the werewolves on which the Worgen are based are lunar creatures. In the most popular mythology they are forced to transform when the moon is full but this is not always the case. Part of this can be seen in the Wolfcult of Northrend's Grizzly Hills who remain in human form until forced into combat. For the Night Elves, who revere the larger silvery orb known as the White Lady as their supreme Goddess, Elune, the Worgen are a part of their mytholgy. While in the past, the Scythe of Elune storyline has been a big part of Worgen lore, how much of it and the pull of the Moon - which is found in traditional werewolf lore - will make it into Cataclysm remains to be seen.
This is part of the excitement of a new expansion, the promise of the unknown is just that, so promising! For a short time, our imaginations can wander without the constraints of fact and detail. We can dream of what we want the Worgen and, specifically, the Druid class to be within the lore of Azeroth. Regardless of what this might be in the end, there is definitely going to be a close bond between the Kaldorei and the people of Gilneas which will shape how World of Warcraft moves into a post-Cataclysm age.