One of the best kept secrets of WWDC is that random conversations and run-ins as well as the official Labs at the conference are where much of the ticket value lies.
You can often learn tons of interesting details just by talking shop with the Apple employees hanging around.
Here's a summary of all the interesting details I learned today:
HomeKit
The new HomeKit triggers don't let you run arbitrary code, you schedule things like "when the garage opens, turn the thermostat to 70 degrees", and then everything happens out of process from your app.
Notifications about property changes on HomeKit devices are only delivered if your app is in the foreground. Great for privacy, but boo.
ReplayKit
Apple is totally fine with developers using this framework to record anything, not just Games. Wondering what interesting use cases (besides the obvious: user testing). This could get really fun.
Developers never get access directly to the video files. They're stored in a system directory and the user is offered the chance to share them with a standard activity view controller once recording completes. You can add custom actions that will appear in the activity view controller that appears though.
GameplayKit
Just like ReplayKit, you're free to use all of the features of GameplayKit for things other than games. Hey look, a free state machine implementation. Thanks Apple! (GameplayKit has a ton of incredbly useful and awesome features, I was just curious about this particular use case.)
Search
Apple has already been crawling the web and looking at things such as existing meta tags that are commonly included on popular websites. They're also noticing if sites have the old (but still great) Smart App Banners feature. When possible, they're tying the information together. If your app is installed, when a user taps on a search result, it deep links you into the app, otherwise, the website and Smart App Banner are shown.
In fact, this system is so far along that I was actually shown a demo of one of the apps I work on completely working as described above already on iOS 9 (since Apple already crawled the website and the meta tags were already configured correctly.) Neat!
Other
Mango Odwalla is delicious.