I thought that too. We don’t really know the exact details yet of what it will be like.
After all, half of the original city has been closed to us forever. If they redesigned that part of it and made it useable, it would signficantly increase the city’s size. Naturally they would adjust it proprortionately (because they do that to the world and the continents each time they add places so I’m sure they’d do the same thing to Silvermoon) but I can’t see any reason why they wouldn’t make use of an area like that. Why leave it as a dead zone when it could be absorbed and fixed up?