If Foundation is to retain binary compatibility with Obj-C, then it will by necessity still be using the Obj-C runtime, with Foundation types still extending NS

If Foundation is to retain binary compatibility with Obj-C, then it will by necessity still be using the Obj-C runtime, with Foundation types still extending NSObject, and thus swizzling should still work as before. The alternative would be for Apple to break compatibility with old Obj-C apps, instead shipping a compatibility version of Foundation.framework which old apps would continue to link against. But it sounds like they're not going that route.