I absolutely hate any guild setup that involves me sinking resources into "guild vaults", it makes leaving a guild or starting a guild hurt the player.
Then adding an element when one guild can take these resources from another, please no.
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I would love to see a punching bag style guild event, runs for X days and there is no Defeating it, just rewards based on how much damage the guild has done in that time.
There are many great battle scenes that could work in a GW style setup for the guild where you either progress through nodes until your team is dead, or face waves upon waves with mini bosses every so often, to achieve a pool of damage for the guild and rewards based on that number.