Form plugin XHR upload?

Hey Mike, any plans on incorporating XHR upload into the form upload,
with a fallback to iframe upload?
See http://hacks.mozilla.org/2009/06/xhr-progress-and-richer-file-uploading-feedback/
Would be interesting to extend the form plugin API with a progress
callback, which gets called just once (on success) for the iframe
fallback.
Jörn