I wouldn’t mind a cross server auction house in the tavern
I wouldn't mind either, I think global trade would be a nice thing, and after an initial price shock everything would settle down and it would be beneficial for the game in the long run.
My main point for supporting the castle over the tavern is the fact that there is a reason for most people to come to the castle. If the tavern had a similar demand then I would support it, but as it stands, the tavern won't last long.
While having a cross trade might seem beneficial, (Hey, I can trade all my items from my old server to my new server instead of selling it back ) in the long run, it would just lead to a huge imbalance of items between worlds that would ultimately kill off less populated servers.
Why would someone enjoying playing in a world where it’s completely stripped of all high tiered gear because it’s all localized in a different server now?
In terms of the global Castle, I definitely did not agree with it. Interaction between different servers shouldn’t be “forced” and players should have access to all the necessary places (bounty boards, auction houses, etc) without having to participate in a global wide area. Yes, the game is technically a “MMO,” but the huge appeal of the game is not the “massively multiplayer” potion of it and players shouldn’t even forced into one area if they don’t want to. (And yes this includes a significant amount of people)
For players who
do want to participate in more global events that doesn’t include just killing each other in arena or tavern, I would seriously recommend some type of cooperative mini game or boss raid “outside” the normal raids done with individual servers/clans. Especially if it has a reward at the end, teaming up with random people from different servers might be an extremely fun thing to do while keeping the uniqueness of every server.