Firstly, huge congratulations to the new core team members. I'm sad to see Dave stepping down, but I hope he'll continue to be active with the language.
One domain that I think is worth keeping an eye on is scripting. Scripts are interesting, because lots of programs start out as scripts. At the same time, Swift is a great language for scripting, because (especially on Darwin systems) lots of system functionality is exposed via Swift. If I have to resize a bunch of images - sure, I could download imagemagick, learn it's complicated command-line interface and fumble around with shell scripts; or, if I'm on a Mac generating images for the AppStore, I could use Swift and the much more pleasant CoreGraphics interface.
It's incredibly common to want to have scripts that perform some action or generate other images based an image's contents. It's really hard to do this without a language like Swift, and it's great because all your code is also written in Swift.
Also - scripts really favour brevity. Not so much in the names of functions and parameters, but in how much boilerplate you need to just get something done. Things like parsing command-line arguments should be way easier than they currently are. Which brings me on to Foundation.
I don't think Foundation has really worked to make Swift a pleasant language to use. Part of that is structural - it has a closed evolution process and is entirely controlled by Apple. The other part is technical - it tries to be a platform-abstraction library over things like sockets and files, but really it's a system library, because it's part of the OS on Darwin platforms. That means Darwin platforms get the worst compatibility story, with
@available and fallbacks everywhere, and the inability to take advantage of new API (e.g. let's say we added a new command-line parsing API - it would be unsupported on all current versions of macOS). I think there is room for a library above Foundation, with a more radically-swifty API and independent versioning.
The original goal was, I think, that Apple platforms would have an optimised version of Foundation because they build Swift in to the OS. That can still be true, and it's great that Apple provides Swift-native generic types and protocols in their OS libraries, but I think the smarter option is to access those fast Foundation APIs via an intermediate library that can float and add new features. Something more like what
I'm very happy to hear that low-level systems haven't been forgotten about