The access modifier of scene.image.Image.url has to be changed from default (script only) to protected, to enable binding it's value to another variable, as it's possible for other Nodes (like Scence.content).
Is this a change request? You should use the issue tracking system instead: http://javafx-jira.kenai.com
But I think you are confusing Image and ImageView. Image just holds the image-data and allowing to change the url later will probably break its functionality. It is not a Node. ImageView is the corresponding Node and its most important member "image" is public.
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