I'm not sure this will work as well as it could or should. While breaking Foundation up seems like the best thing long term for the framework and Swift, it needs to be into multiple modules organized in a dependency tree that can share common types. I'm not familiar enough with all Foundation types to say what that tree would look like, but it would be far more than just a Foundation / Lite / URLSession separation while still under the Foundation umbrella.
I'm also not sure how much effort we should be putting in here, as, to my eyes, Foundation is a temporary compatibility and bootstrapping solution for Swift, not what we want these types and functionality to look like long term. But I guess as long as everything stays under the Foundation umbrella, Swift is free to create it's own replacement types and functionality at some point in the future.