If you look out long term, Ishguard will likely become the next central hub just as Jeuno was for FFXI. (Aht Urgan eventually became the next, but it's connection to Jeuno and the other 3 cities through the warp taru was the primary reason for this). With all the content that surrounds Ishguard I'd imagine there are things the devs are planning to address each of these issues that otherwise cannot be talked about.

But, I am in favor of a linking of the market wards. Mainly to help facilitate newer players and give the option for other players to play effectively from each of the cities.