The review of SE-0027 "Expose code unit initializers on String” ran from February 11…16, 2016. The proposal has been rejected.
swift-evolution/0027-string-from-code-units.md at master · apple/swift-evolution · GitHub
At this point, the core team feels that we have not fully explored the design space here, and that known alternatives (e.g., making the UTF-16 and UTF-32 views of a String mutable collections) might provide a better long-term solution. Moreover, the String type itself is undergoing a significant re-evaluation, so the core team feels that improvements to String should be delayed until the newer design is better understood.
Doug Gregor
Review Manager