Why though?
The population of the 9 realms all combined are still going to be less than Hyjal, and since Blade’s Edge / Thunderhorn is slightly Alliance heavy and Agamaggan / Archimonde / Burning Legion / Jaedenar / Kargath / Norgannon / The Underbog is Horde heavy the connection could be a good thing.
There’s even a thread where several players from those servers claiming that their servers felt dead.