If you're clever enough you can poke around in app files to find clues to forthcoming functionality - features the developers are laying the foundations for but haven't yet unveiled to the world at large.
Android Police has been hunting through v4.8 of the Google app (which holds Google Now, the "OK Google" search and more) and have found code that points to an offline mode coming soon.
That means you might be able to perform certain actions without Wi-Fi or a data connection. Obviously web searches aren't likely to be included unless Google is going to cache the entire internet on your phone.
Android Police says the offline "OK Google" will be able to make a call, send a text, play some music and turn on Wi-Fi on demand, with Google probably planning to add more options in the future.
Apparently the app code also suggests that volume and brightness controls will soon be accessible just by talking, so you can mute your phone or dim its screen with a shout at your handset.
As Android Police notes, you shouldn't take any of this as set in stone: Google may well be testing features that it later pulls. But with Cortana and Siri improving all the time, "OK Google" and Google Now can't afford to stand still.