This feature may only be available with phones with dedicated hardware.
Slashgear reports that a recent leaked build of Android 4.4 "KatKat" references to homepage-based "OK Google Now" abilities, meaning the platform will support phones that can "listen" for commands without draining the life of the battery. Currently, the ability to speak commands is limited to the speaker button on the Google Search widget and within the Google Search app itself.
The news is based on a leak of an Italian build of the LG-made Nexus 5 running Android 4.4, which was capable of responding to "OK Google" or "OK Google Now" from the homescreen. This device is supposedly shipping with Qualcomm's Snapdragon 800 chip featuring the company's Snapdragon Voice Activation tech.
The report also points to Motorola's Moto X phone that uses the Motorola X8 compute system for voice activation even when the phone screen is off. There's a unique CPU core dedicated specifically to low-power listening, thus the phone's battery isn't eaten alive as the device sits and listens for the next user command.
That said, this "listening" ability will likely be introduced on the Nexus 5, and a feature not every Android phone will support. That is, of course, if Google hasn't teamed up with device makers to optimize this app in such a way that the battery drain is minimal. This "listening" feature may also be an Android 4.4 feature exclusive anyway, excluding many devices.
AndroidPolice also reports that Google is actually releasing a new "Google Experience" launcher within Android 4.4, and possibly as a free, standalone app on Google Play for those who want to ditch the manufacturer's custom interface. The brand itself will also include other components -- like the Google Keyboard for instance -- that users can install to make their device more Google-like.
The report clarifies that Google Search/Now is integrated deep within Google Experience, and has a permanent home on the very left home screen. This screen features a one-touch button to set a reminder, and the Search's voice input prompt is now somewhat transparent on the bottom and floats instead of occupying the whole screen.