A small detail from some screenshots in the keynotes (and later confirmed on Apple's website) is adding next-hour precipitation to the native weather apps for both iOS and MacOS:

If I could take a guess, it looks like they've already integrated DarkSky's forecasts into iOS. It's a relief for any of us who have been desparately seeking a weather app that has good data + isn't bloated with all sorts of nonsense/distractions, but still a bummer that Dark Sky isn't its own company anymore.