I have a small library of immutable collections (Tuple, OrderedList, HashMap plus type-safe versions of OrderedList and HashMap) at https://github.com/DavidArno/AS3Immutable. I'd be more than happy to donate these if we did want to build a set of collection classes into the SDK. They'd probably need a bit of work on them to make them faster as I wasn't interested in speed when I wrote them though.
And hopefully generics will be supported by the Falcon compiler. I know I'm planning it with my Goshawk efforts. David.
