I'd like to see a separation between read and write permissions to the DOM for plugins personally. I would feel much better if I didn't have to give any plugin that might need to modify parts of a limited set of pages the ability to silently manipulate anything and everything I see in the browser. Read-only access could be granted by default, then only when a plugin sees something it wants to act on it could pop up and request my approval before doing so. The current approximation of that by disabling the plugin globally and enabling it on specific pages is so clunky and adds so much extra friction that I don't ever bother with it.