The best stuff that we're not going to get, is everything above the STL, but I doubt anyone is expecting that Foundation/Cocoa are going to get open sourced any time soon :)
Here are some other users who may feel they are getting the "best stuff":
Compiler designers, programming language researchers, or even CS students the Swift core is a fount of of information to learn from, modify, experiment.
Teachers whose school could not afford Macs. They can now use Swift on cheap Linux machines, and eventually on Windows.
