Flex has been part of the Open Source community since the release of Flex 3. What's different now is that Adobe has released the roadmap for Flex, relinquishing control of the SDK to the community at large.  Adobe plans to be part of that community, rather than being the controlling body.  There are still some issues with this approach since Adobe is not opening up the Flash Player to the Open Source community.  When trying to build a platform that is dependent on the Flash Player and you don’t know the underlying features, it makes it difficult to extend past the current release.