The sollution is simple. First, add portals to new zones from all the capitals. The reason why players don't sit in them isn't because they're bad, it's because of convenience, the transmog npcs are in SW/ORG, the portals are in SW/ORG, the reforge are in SW/ORG... why? Put them in the other cities too.
No room? Well then put one portal, when someone selects it, they're given options of where to go.
Also, they can start with old cities. Ironforge and Undercity first since they were the most populated after SW and ORG, then Darnassus and Thunder Bluff, and last, but not least, Exodar and Silvermoon.