Update: We've looked into this further and it turns out you might have to wait longer for yoga tracking - this reference in the file is apparently about new labels for optional, manual workouts you can program yourself on Apple Watch, not about automatic tracking for yoga. Control of external yoga apps will still be on the table in Watch OS 4 though.
News continues to leak out about what's new in iPhone 8, and most of those rumors seem to be coming from a leaked iOS release related to the HomePod speaker. Something else we were tipped to in that same file: several references to yoga, including under a listing of workouts associated with the Apple Watch.
While the yoga listing (right under "walk" and before "crosstraining") isn't directly connected with the Watch, the list includes many of the typical workouts associated with workouts on the Watch.
Downhill skiing also makes an appearance in that same list, something MacRumors has mentioned could be coming to Apple Watch.
Yoga shows up 29 times in the file; many of these are references to websites. However, the file also mentions some interesting findings, such as "Workout Activity Type," "doing Yoga" and "yoga Prototype."
So far Apple has required Watch owners to manually enter yoga and other not-yet-added activities as "other" in the workouts menu.
Yoga is probably tough to track through a device on your arm as it requires interpreting a lot of slow movements. There don't seem to be many workout trackers that have added yoga as a listed choice for likely that reason. But other uses for the Watch during yoga could be remote control of instructional videos or apps.
Fitbit offers the ability to add yoga as a workout for some of its devices, but it's not automatically on its list of workout activities — you have to set it up as a preferred workout first. Misfit's app also claims to include yoga as an activity for its Shine device, but you must first set up a "tag" for yoga. It's unclear how accurate these trackers are at interpreting yoga movements, but a few Fitbit users have voiced their confusion over the process.
Apple declined to comment and has not confirmed it will be adding yoga as a workout, but has announced it will include HIIT, or high-intensity interval training, in the WatchOS 4 roll out, along with a Siri activity coach, the addition of GymKit and an "enhanced Workout app."