However, I kind of like the sound of this event.
Just a note: keep a thread open with active updates on progress in Gilneas. Maybe take a map and highlight areas that have been 'reclaimed' and continue to update the map as the event progresses. Keep it posted on the thread. There is no need to rush it within a couple of weeks, either. Take some time between each push into Gilneas. Establish a foothold. Consistently RP inbetween your invasions.
Also: open it to more than just Worgen. To my knowledge, the 7th Legion is currently there already, so it wouldn't be out of the norm for non-Gilneans to offer helping hands. Considering that you would be fighting Horde in Gilneas, you would have quite a few helping hands.
Finally, I'm sure you are already aware of this and will do well to avoid it, but avoid establishing authority in Gilneas. Everything is done in the name of Greymane, and he should be taking full credit for the reclamation regardless of his presence.
I only approve of this because I don't see Blizzard actually doing anything with Gilneas in the future, and think that it is destined to remain empty and forgotten.