Hi there, excellent question!
Right now we're actually working on making your requested functionality an integral part of Spring Actionscript which will be included in the upcoming v0.9 release.
If you check out the trunk in SVN the required functionality is already available. One thing you have to make sure of though when you're loading modules into your application and want them to live in their own ApplicationDomain is to create their ApplicationDomain with the main ApplicationDomain as its parent.
So, a rough example in actionscript would be this:
That way the applicationContext of the main application will be able to autowire components inside your module, while the module can still be safely unloaded afterwards. (Since it has its own app domain).
var moduleLoader:ModuleLoader = new ModuleLoader();
moduleLoader.applicationDomain = new ApplicationDomain(ApplicationDomain.currentDomain);
Also available in the trunk is the possibility for an application context to have a parent context. So in a multi-module scenario you can give each module its own app context with the main application context set as its parent.
This gives you the ability to either have the main application context create or autowire your objects, or the module application context itself. We also support overriding of object definitions. So if a module context has an object definition with the same name as an object definition in its parent context, the child context will override.
If you check out the sample app in the trunk called \spring-actionscript-core\samples\multiple-modules you can see a simple example of such a scenario. The main application has a context and two modules are loaded in separate domains and have autowiring definitions defined inside their own configuration but can also fall back on the parent context.
Right, I hope this all sort of makes sense, I'll be working on a documentation section about this, I hope I'll make it a bit more clear than the above story
Anyways, just check out the sample app, I think the code and configuration speak for itself.
If you have any questions then of course we'll be glad to answer them.
P.S. since this is trunk code, please bear in mind its still rather beta. I'm using it in my current project, so I'm quite confident that it works pretty well, but should you run into any issues, please let me know a.s.a.p. so we can solve it before we have an official v0.9 release.