The review of "SE-0144: Allow Single Dollar Sign as a Valid Identifier" ran from October 14...18. The proposal has been *rejected*.
The majority of the feedback on this proposal was opposed to it, because it makes the Swift language complex for a single library. While it is unfortunate that this library is out in the wild and that there are some users, it was never intended for a single dollar sign to be allowed as an identifier, and it was also never documented as such. The core team believes that Swift 3 compatibility mode will be able to cleanly handle compatibility issues implied by not accepting this proposal.
Thank you to Ankur Patel for raising this proposal: it was important to get proper community discussion and feedback on this topic.