It is an integral part of the Swift project (and toolchain too, once integration is complete). Bugs go at bugs.swift.org. Feature development belong here on the forums.
The last official word I recall was the following, which indicates that discussions about engineering improvements belong in the Development category, (which is where they have been happening). Discussion about the style guide itself has never really resumed that I know of. I think that is because the team has so far been focused on integration and performance instead. When it does pick up again, it sounds like it will be a matter for the evolution process (pitch → proposal → review).
I suspect the team would be likely to accept a pull request that adds an adaptation of the Support section from the SwiftPM repository.