Basically the same issue about Flex SDK configuration

The Flex sources could even be caught up iff belong for dependent module

I think that at the moment Flex SDK does not contain all sources, only sources for a small subset of the base libraries - only "mx.*" packages.
So a stub generator for compiled classes/libraries would still be very valuable.

My understanding is that "mx.*" is not a small subset of the base libraries but more like 80% of them. The remaining 20% in the flash.* namespace is indeed not open-source, but I could somewhat live without navigation/completion for them. :)

The problem is not with navigation but with inherited members from nonopen api :)

You can browse for yourself, here is online asdoc / javadoc for Flex 2.0 SDK: http://livedocs.adobe.com/flex/2/langref/

Note that:

• A lot of the mx.* packages are mainly used by the Flex designer
  
• Most of the flash.* packages are quite "central" in terms of type dependencies. Comparing it to java.* / javax.* is not good analogy, but something like that...

Additional thoughts:

• Adobe announced open source release of Flex 3.0 SDK, I don't know if that will include complete framework source (and if it will be 2007 or more like 2008)
  
• Some third-party Flex libraries are distributed in compiled form (.swc - similar to .jar), so a constant-pool reader / stub generator will "always" be needed

In addition (but a bit off-topic) - here's a list of some as3 / es4 incompatibilities: http://developer.mozilla.org/es4/clarification/adobe_as3.html