hey eco,
I mentioned the idea in this thread:
http://forums.puremvc.org/index.php?topic=1658.0 but I haven't tried it yet. Basically if you want to maintain strong typing I believe that you can make your components implement an interface and then just import that interface in your main.swf and type the loaded swf/component to that. I think things get tricky when dealing with events that your component might dispatch. Hopefully they're just in a separate class file which you can also import, otherwise you might want to check out this blog post about a hypothetical way to put events in interfaces. Though the summary of the article basically ends up by saying 'you can put events in interfaces, but it's probably better to just use AS3 Signals'
http://www.davidarno.org/2010/02/24/actionscript-signals-events-and-interfaces/