One feature I would enjoy is a Guild Vault. This is how it would work:

• Guilds purchase a guild vault and/or additional storage space for it for massive fees (much the way they purchase vendors).
  
• Any guild member can donate an item to the vault. Once the item is donated it permanently becomes property of the guild (as in the donating party loses all personal claims to it). However, the donating player's name is inscribed on the item (for example, if I donated Brohn's Holy Rod, its description would be Brohn's Holy Rod [donated by Ronduwil the Red]) just for bragging rights.
  
• Any guild member can check an item out of the vault, but there are some strings (good and bad) attached to it:
  
  1. The item cannot be dropped, sold, salvaged, stored or traded. There are only two valid locations for it: back in the vault and the inventory of the player who checked it out.
     
  2. As the last statement implies, the item can be checked back into the vault by going back to the guildhall and putting it back.
     
  3. Whenever a player logs out, any guild items they were holding automatically go back to the vault.
     
  4. Guild items get the "customized" bonus when they are used.
• The guild leader and/or officers may purge items from the vault at their discretion. Purged items go away forever. This is to prevent people from maliciously filling the vault with crappy items.
  

I don't think this would be very hard to implement, and it would help emphasize the "Guild" in Guild Wars.

I am also puzzled by the "good PvE options for Mesmers" remark. The Energy Surge nerf probably hurt a bit, but my experience with Mesmers is that they are one of the most powerful classes there is (particularly in the late game).

The auction house would be nice, but I can see how it would be difficult to implement. How long would an auction stay good for? How many items can each player auction at a time? How long would it take the game to search for the item you wanted? There are serious concerns with scalability involved. They are not insurmountable, but I would prefer for the emphasis to stay on gameplay rather than on an online vending system. If the choice was between hosting an auction and hosting more alliance battles, I'd take the latter.