Android Wear showed a bit of life a few weeks ago when it was rebranded to "Wear OS by Google," and today it's getting a new Developer Preview based on Android P. Besides the upgrade to a newer version of Android, there are a few new features outlined in Google's blog post.
First, Google is switching to a default "Dark UI system theme." While Android Wear 1.0 sported Google's usual white background with black text, Android Wear 2.0 did a good job of making everything pretty dark. This change will probably clean up some odds and ends that still had a white background.
Background activity for apps is being limited almost completely. Google flatly states that "apps will no longer be allowed to run in the background unless the watch is on the charger," and it tells developers to "remove background services" from their apps. It's hard to come up with an example of a "background" functionality for an Android Wear app. Push notifications should be unaffected, and apps like fitness trackers or music players that generate an ongoing notification don't count as "background" apps. There's an exemption for watch faces and add-in complications, too.
To further increase battery life, Bluetooth, Wi-Fi, and cellular radios will shut down when the watch detects it is no longer on your wrist. This is essentially "airplane mode" and will totally disconnect the watch from the Internet when you aren't wearing it.
The real shock for this Android Wear developer preview is the device compatibility. The only device it works with is the Huawei Watch 2 (available in "regular" and "Classic" designs). The current flagship of the Wear OS market is the Android Wear 2.0 launch device, the LG Watch Sport. This device was designed as a collaboration between LG and Google, which is proudly spelled out on the box via a "Designed with our friends at Google" slogan. Any Android Wear observer would have expected the device with Google co-branding to get the developer preview, but instead, the update is only compatible with Huawei's completely forgettable smartwatch. Both watches are about a year old, so age doesn't seem to be an issue. It's just a complete mystery.
You can download the Wear OS preview for the Huawei Watch 2 here. There's also an emulator image available through the Android SDK. None of these changes sound like the big improvement that wear OS needs, and there's still no major new hardware on the horizon that we know about. At least it's something, though.