Grant Skinner and his team are great but if I have understood it correctly Adobe is working on something similar at the moment where you would compile AS3 to js canvas calls (and more). What today are Flash tools could very well turn out to be the canvas dev environments that are sorely needed. Say what you will about the Flash Player but AS3 is a tidy language, very well suited for this kind of work..
It's really great to see the best Flash devs contributing back to JS/HTML5. This is a perfect application of using skills learned from Flash to make a really great lib.
On the SpriteSheet page they say, "Unrelated to the Sprite display object." --- what Sprite object are they referring to? I don't see one in their API?