Even though Apple has not yet released a beta for new watchOS system software, it has shared some notes about it, with additions including SiriKit on the Apple Watch, and Theater Mode being implemented in it and not the iPhone as previously rumored.
SiriKit has been available on the iPhone and iPad since iOS 10 was released. In addition to extending Siri's support for messaging, photo search and phone calls to more apps when paired with an iPhone, SiriKit also adds support for new services, including ride booking and personal payments.
With SiriKit, Apple is using its App Extension mechanism to allow third party developers to build new support for Siri into their apps by registering "domains" and "intents" they can handle. Within each domain, Siri interprets user "intents" -- what it understands the user wants to accomplish -- and passes this to the app to handle.
"Theater Mode" was first lleaked in late-December as a feature for the iPhone, and it appears it will allow Apple Watch owners to disable the "rise to wake" function on the watch, but still notify users with haptic feedback of notifications without illuminating the watch. A subsequent tap on the watch face will wake the watch.
Apple has given no indication when the Apple Watch beta release will be made available. Betas for macOS 10.12.4, iOS 10.3, and tvOS 10.2 were made on early Tuesday afternoon, only a day after full OS releases.