Shumway makes it sound like "we got this" (which then discourages someone like me--someone who has a ton of knowledge of compiler design and a lot of background specifically with JavaScript-based language but almost no interest in duplicating effort, someone who would normally see this call to action and go "oh, I'll add this to my todo list"--from even spending much time researching the current space). Are you saying Shumway only "barely" supports ActionScript?
There are several such projects - swfdec, lightspark, gnash, etc. From what I've seen of them, they all underestimated the amount of effort. Most of them just petered out. So if you're going for it, I would worry less about duplicating effort and more about setting realistic goals for the project.
