I would like to see the new guild halls to be plot of lands you can buy with influence. You will expand on more land/buildings through the use of influence, making huge amounts of influence still interesting for huge guilds. The concept of the guild halls in Guild Wars 1 will be improved with the idea of a dynamic environment. With the option to build your own guild halls it makes future guild vs guild fights much more interesting, especially since different designs per guild make fights always interesting and new. Giving the guild vs guild concept a new dimension.
You can create your own crafting stations which give more XP and crafting success to members. Buy/hire traders for all sorts of materials, guild armor and guild weapons at a discount. Profession trainers and an ambassador for the trading post. A PvP NPC which give access to WvW and sPvP. A big treasure trove giving an appearance of the wealth. A practice field with dummies to practice your fighting style.
We are already able to capture forts, outposts, keeps and castles. But it would feel rewarding, awesome and grand to have your own place for the guild which would give a good impression how good your guild fares. Think about the size, decoration, creativity and authenticity you can give to players.
Half of Tyria is still open to new maps, which might be a good opportunity to use the unearthed lands to make as possible spots of land for the guildhall. The entrance to the guild hall would be a portal within the home instance of every city. With you own house within the area (which is more realistic and appropriate), while a portal close by leads you to the guild hall/plot of land somewhere within the map. Just like in guild wars 1, these plots of land will, when most guilds have gotten started, being opened up for guild versus guild fights.
I know that many of those things have already been done in Guild Wars 1, but I hope that the suggestion for open design and dynamic environment for your guild halls will be one which will be added in the future. It would add a lot of value to the game and give something unique back to the players that made Guild Wars 1 stand out in comparison to other MMO’s.