If using a multiple world add-on, allow an option in the config file to support per-world accounts. Personally fine with the existing settings being global (same currency, but not shared accounts). Some multi-world solutions allow you to restrict inventories to per world, which makes Gringott's a great asset, but currently only if you prohibit use of the commands to interact with vaults.

Woops - dupe of issue #74 - MultiWorld support.

Yep :)
As a workaround, if you can do without the chest and enderchest vaults, you can disable them globally, and use only the inventory money.