The second review of "SE-0110: Distinguish between single-tuple and multiple-argument function types " ran from June 30 ... July 4, 2016. The proposal has been *accepted*:
The community and core team agree that this proposal is the right thing to do, and many agree that this could probably have been treated as a bug fix on a previous proposal.
Thank you to Vladimir S. and Austin Zheng for driving this discussion forward! I filed SR-2008 to track implementation work on this, this would be a great area for someone interested in the type checker to dive into the Swift compiler.