Shield Tablet K1 . . Those Android changes include repostioned landscape mode navigation buttons, updated emojis, a quick-launch camera feature that's invoked with a double-press of the home button, and a do-not-disturb-until-next-alarm mode.
Android security patches through March 1, 2016 are also included in this firmware update. Other minor-but-notable improvements include support for Android 6.0's Doze mode and enhanced memory compression. The full list of fixes and improvements is available on Nvidia's forums in this feedback thread. A follow-up release for this updated firmware is claimed to be in the works for older Shield Tablets, too. Nvidia says it'll arrive in a few weeks.