Update: Google says Now Launcher is available for all Android 4.1+ devices:
(@Android) August 01, 2014
It looks like the Google Now Launcher might soon be available on a long list of new devices as a small update to the app brings reports of expanded compatibility for a number of notable Android phones. AndroidCentral points us to users seeing compatibility with devices including the LG G3, Verizon’s Galaxy S5, the HTC One M8, One E8, One Mini 2, Desire 816, and the Huawei Ascend P7.
The expanded compatibility isn’t officially included in the release notes nor has Google officially made an announcement, but we expect to hear more shortly. The Google Now launcher, which was previously only available for Nexus and Google Play Edition devices, adds Google Now to the home screen for a more integrated experience with the OS.
The Google Now Launcher is available on Google Play here.