Regarding the topic of back deployment: whether or not a part of the Swift standard library will be back deployed is a decision for the platform vendor, not something that is part of the evolution review. It won't be decided here in this thread.
I get the reason, but doesn't it hurt Swift's image outside Apple's platforms?
The issue of back deployment only matters on ABI-stable platforms (currently only Apple platforms). On other non-ABI-stable platforms, this is a non-issue.