The best part? "Sweet baby titans!" I'm going to find a way to work that phrase into daily conversations from now on. Boytoy is not going to be amused...
Having actually read up on the whole thing, what players will do is aid in the retaking before Cata, and it will just be assumed in that three (?) year timespan all those players going to help would have just done it on it's own, no huge big wave and push. There isn't going to be a retaking if the capital city for gnomes changes to Gnomergan because it'd just be too hard for new gnomes to get into it.
tl;dr It's not some huge event, it's just having players run quests as if they are helping to retake it.
I have a very sad, sneaking suspicion that they are doing this -just- before they destroy the Echo Isles and Gnomer in Cataclysm. So they can say "well, look at that... isn't that just sad?"
I think they'd made a big deal out of it they were gonna add new cities to the game, Anski is probably right, they'll just change/add quests to make it feel more like there is an effort to reclaim the areas before Cataclysm, then they'll both be blown to smithereens, or sunk.
I thought it'd be at least a bit deeper.