However as it continues to be said, this is not GW1, and the things Guild Halls were useful for (i.e. easy access to things like Material Traders, Rare Material Traders, Rune Traders, etc) do not exist in GW2, instead we have the Trading Post. As such, the institutions that Guild Halls used to be good for, do not exist in GW2, as such, the comparison cannot be accurately made.
Realistically speaking, what would you want a Guild Hall for, that you cannot readily access anywhere else? It's worth noting as well that the social aspects of cities in GW2 is very enjoyable, so think about if Guild Halls were brought in with every possible merchant, a bank, a trading post representative. Would that not significantly affect the amount of people who choose to go to those cities?
I've given this situation some deep thought, and I think I've found a win-win for both the players and NCSoft.
First, have the current pirates content end in a cove/cave with an epic battle where a stray cannon ball (fired from the top of a domesticated karka cannon walker, naturally) opens a passage revealing an ancient guild hall. This can allow the next phase of the Living Story: Bindi Banana Jones and the Secrets of Ascalon, a story of archeological intrigue and mystery that is sure to have players log back into the game for at least a week.
Have the newly revealed guild hall be overrun by Skritt and Dredge who, when slain, have a chance of dropping Promising Objects of Significance. Ten thousand objects could be turned into an archaeological NPC for a special back piece that glows in the dark. As a bonus, make the enemies easy to kill so that players feel as if they are competing with each other for the drop chance, artificially increasing its rarity. Achievements could include: (1) scrubbing 500 ancient artifacts for overworked digsite assistants, (2) using an Asura decoding device to "translate" 150 ancient tablets and scrolls of "profound significance," (3) polishing ancient weapons of "immense power," (4) slaying 300 Skritt, (5) slaying 300 Dredge.
All this will be backdrop for the new and exciting Strange Cryptic Antiquarian Mystery chest. Each chest would contain some ancient ascalonian beverage (+10% Karma Boost for 10 Minutes), a chance at a bag of ancient coins that can be vendored for 5 silver, and a (rare) chance at a guild hall token, which could be delivered to the archeology NPC to set up your very own guild hall! A different version, the Rich New Golden Strange Cryptic Antiquarian Mystery chest, with a higher token drop rate, could be sold in the cash shop for 1,500 gems.
Each guild hall feature could then be sold at a reasonable gem price, or even
Finally, each character would require a unique Guild Hall Stone for every guild of which a player is a member. This would incentivize players to purchase more bank slots.
As I said, win-win for everyone.