Thanks for this work, it's quite interesting to see such developments and I agree with @MarkTraceur (WMF) that the current upload pipeline is very 2003 :-)
My only concern is where in the pipeline this fits and what happens to the original file (compare from @Pginer-WMF's comment on ability to go back to the original). My reason for wanting to make sure of this is that when you process an image through Canvas in this way, you lose any metadata that was embedded in the original: EXIF information and similar. Retaining this information is non-trivial and would require too much work to work in the general case, and so fitting this editor in the pipeline in such a way that the original file is still retained on the wiki would probably be the most sensible thing.
It's entirely possible that this was the intention all along and I just didn't pay enough attention :-)