The “Marshall Plan” is the nickname for the SDK feature to support cross-versioning.
The nickname comes from the aspect of the feature that uses shared events and/or the SandboxBridge to marshal objects across ApplicationDomains. Marshalling was popularized in Windows as a way of transcoding objects so they can be shared between applications in different address spaces.
If the vision comes true, the “Marshall Plan” will define a post-3.1 Flex that liberate developers from having to have all of their code compiled by the same version of Flex.
Read more about this initiative which are planned to be part of the Flex 4 release.