Linking the AH's in XI helped populate the other towns i believe.

Plus when we have airships, i think we will see another increase in the population since 1.18 (Guild Marks only from cities with the guild.)

So maybe linking AH's will help. Influx of new players too will repopulate the area. Grid was very very busy during the first few weeks of the game on Gyshal. But died down as players progressed in the story, sending them to Ul'dah. Then the whole abandon leve thing caused players to stick in Ul'dah.

But basically like Xatsh said ppl will flock to Ishguard when it opens up and we wont see any players in the cities at all.