I think it may be possibly to convert a Synfig project into and SWF by using XSL or something similar to change *.sif files into *.xml files (the SWFML dialect) usable by “swfmill”. I’m going to experiment with it 
Sounds cool and usable! Keep us updated on your progress.
I’ve set up a Git repository at https://github.com/ChillyCider/sif2swfml. I’ll be honest, I don’t know much of XSL. If it works as expected soon, one would be able to turn Synfig files into Flash symbols for use in Flash animation.
Ah, so it’s an intermediate format? Not for publishing flash files on the web?
Yes… sorry ^_^. I currently don’t know the extent of SWFML’s power, so I don’t know if exporting to an animation would be easy to do.