While snooping around the APK for the Google Clock app included in the latest Android O Beta, I noticed the following definitions in the app's AndroidManifest.xml:

<meta-data 
  android:name="com.google.android.apps.nexuslauncher.LEVEL_PER_TICK_ICON_ROUND" 
  android:resource="@mipmap/launcher_clock"/>
<meta-data 
  android:name="com.google.android.apps.nexuslauncher.HOUR_LAYER_INDEX 
  android:value="1"/>
<meta-data 
  android:name="com.google.android.apps.nexuslauncher.MINUTE_LAYER_INDEX"
  android:value="2"/>
<meta-data 
  android:name="com.google.android.apps.nexuslauncher.SECOND_LAYER_INDEX"
  android:value="3"/>
<meta-data 
  android:name="com.google.android.apps.nexuslauncher.DEFAULT_HOUR" 
  android:value="10"/>
<meta-data 
  android:name="com.google.android.apps.nexuslauncher.DEFAULT_MINUTE" 
  android:value="10"/>
<meta-data 
  android:name="com.google.android.apps.nexuslauncher.DEFAULT_SECOND" 
  android:value="30"/>

Furthermore, the app APK contains the the following images:

1 + 1 = an animated clock icon

Given the above, all signs very much point to Pixel Launcher soon supporting an animated clock icon for the Google Clock app.

As of the July 2017 update, this animated clock icon displays in Action Launcher for the Google Clock app, for desktop shortcuts as well as in the All Apps drawer.

As a bonus, this animated clock is also available in Action Launcher as a standalone widget:

Animated clocks are available in Action Launcher's 25.0 update, which is out now. Grab it from the Play Store.