Thank you devs and GMs for keeping our game healthy over 20+ years. Would it be possible, someday when you're in the area, to get a widget on the guild bank panel to set all items public? Or even a default access mode when adding items? For those of us who have a private guild to store and trade items among our toons, it would save a bunch of mouse clicks.
I think you will need to use houses as storage to store and trade between guild mates. Would hold far more than the bank anyway. I have some set up in the hood under the guild hall so its just a short drop to them. Just give everyone access. This works well for the F2P folks that don't have all the guild hall rights for interacting too If they changed that in the guild hall it would tick off a lot of guilds that are very public and have strict rules etc on who can get what out of the bank. And there are some not so good players in the game that join guilds just to wipe out the guild banks.
Take it from someone who's tried the guild bank system to hold your own private stuff. The guild bank system is just not made for the kind of interactions you will be wanting. As CatsPaws said, you will want to take advantage of the housing system. Far more control over who can access (especially if you have a few toons in non-private guilds) and more space to store stuff. I'm not saying your ideas are bad (most of us have wished for something similar at some point ... at least those who tried to use the guild banks for personal storage), but in the long run they just won't matter. You will be far happier committing to the housing system as your "banks" and not the guild bank.
