Up until now, this kind of functionality has been fairly limited beyond solutions like Miracast, as well as being very similar to features being brought to Cyanogen Mod 11 with AirPlay.
Google's popular Chromecast dongle allows for Chrome browser tabs to be beamed to the big screen, but as you likely know, only officially supported apps have that functionality at this point on mobile devices.
Dutta found information regarding APIs related to capturing video output from an Android device, but that the system doesn't appear to be as open ended as we might we have liked. He says that only approved devices appear as though they will be supported, meaning we might not be able to use other hardware like a Roku box or an Apple TV as receivers.
"From the patches I see in 4.4.1, they'll be adding Android mirroring to Chromecast very soon," Dutta wrote on his Google+ account. "Unfortunately that API is not available to anyone but Google and the OEM. Similar solutions to different hardware can't be built..."
While this feature and the Cast SDK will likely open things up on the mobile side, it doesn't come to much surprise that Google would lock down the hardware receiver end. Although there is nothing official at this point, some reports are suggesting we could be seeing these new features alongside the release of the SDK, which is expected some time this month.