I'd really appreciate if there was some sort of informative event that was thrown when a plugin uses Inventory#addItem() and similar methods that modify the state of an inventory. It should contain the affected inventory. This method would be useful for plugins that need to keep an inventory monitored and tag items as they are added. It's not currently achievable as far as I am aware and the only workarounds are runnables (memory intensive) or piggybacking on an event (unpredictable).