Add drag and drop hooks in the view API to allow plugins to define custom behavior when a file is dragged in. This could be used to, for example, add a relative path to an image file in your html text.
Obviously, there should be a way to maintain the default behavior. One idea is that dragging to the tab bar will always open the file with the default view. Another idea is that the API hook can accept a False return value, meaning that the plugin looked at the file but decided to not do anything with it.