Update: It's not true! Brad says they will use PowerCollections!
Brad Abrams admits in a post that from the responders to a posting asking direction for generic collections, including Don Box (and yours truly), he got very clear direction. Did the BCL team get right on it? Nope. They shoved it off into a community project, Power Collections, managed by Wintellect and led by Peter Golde. Boo-hiss. I'm reminded of Bjarne Stroustrup's comments in his tome about the C++ Standard Library string class: “You have issues with it, I have issues with it, but at least it's standard.” (Not a direct quote)
There's the key thing missing from the “great” community effort. Collections are fundamental to object-oriented development, it's very hard to make core enterprise code dependent on unsupported “community” products. Any guarantees from the BCL team of adopting the results? I didn't see any.
Still I would keep a keen eye on Power Collections.