In order to free up the Flex SDK to move forward, I'm thinking it would be advantageous to split the SDK into "Flex-Core" and "Flex-More" like Merb (a Ruby library that merged with Rails).
This would mean that the compiler, standard libraries and core components could move forward in versions more freely, eg. without fringe components necessarily being updated. Also popular third party libraries could more easily be included into Flex-More. When it comes time for FalconJS, it could aim to support just the components in Flex-Core to begin with, and projects too could just depend on it without Flex-More. This would be easier to manage too if a package manager became a core component as previously suggested, in fact it would make it easy to break the SDK into even more chunks.
