Fully redesigned source editor: You can now increase and decrease the source editor font using Command-plus and Command-minus. I have been waiting for this for years. Other highlights include an improved find and replace system, better scrolling, and integrated markdown support.
Better refactoring. Global renaming works across Swift, ObjC, IB, and other file types. Apple says you can view changes in a unified presentation. The naming strategies for properties, getters, setters, and synthesized ivars are all coordinated.
Better boilerplate. “Fix-it automatically fills in missing cases in switch statements, and mandatory methods for protocol conformance with one click.”
Better Assets including Named Colors. Support for named colors, wide-gamut icons, HEIF images (the ones they discussed during the keynote this morning), and of course, the larger iOS Marketing images. I suspect “Added option to preserve image vector data for matching Dynamic Type scaling” won’t be as exciting as I’d hope, but I’m looking forward to finding out more.
Github Integration. “GitHub account integration for easy browsing and one-click creation of a project and the associated GitHub repository.”
First class playgrounds. New playground templates designed to run (depending on the target) on macOS, in the simulator, and on iOS Swift Playgrounds. If you’re looking for them, choose File > New > Playground. They’re not in “File > New” anymore.