I was thinking what could be the new home of the night elves, first I thought it could be Duskwood its place has a Great tree that gives them a portal to the emerald dream and the atmosphere is very similar to the environment that the night elves are accustomed It is also very close to their main allies humans to protect them. I think it would be a perfect place
but then I thought about val'sharah it is already an night elf territory has everything that represents the culture of the night elves and they would not have to start from 0, It is a place with a strong Druid connection, with many forests and the temple of Elune which symbolizes the strong religious culture of the night elves and many places that can be repaired and used to people Dreamgrove, Black Rook Hold, Temple of Elune, Shaladrassil, etc and they could still have a connection with the gilneans of Bradensbrook.
Another important point is that if val'sharah becomes the night elf power center will be able to counteract to suramar and highmountain in this way it could prevent all the Broken Isles from being under the control of the horde