Google NASDAQ:GOOGL) NASDAQ:GOOG) Apple NASDAQ:AAPL) Thanks largely to its relative affordability, ease of use, and an ever-increasing selection of supported media streaming apps,Chromecast has proven a huge success so far. But one impending feature could take Chromecast to a whole new level -- and threatenTV in the process.

At Google I/O 2014 last week, Rishi Chandra, Google Chromecast's director of product management, revealed full-display mirroring will soon be available on Chromecast for many of the world's most popular Android devices. Initially, that includes only Samsung's Galaxy Note3, Galaxy S4 and S5, two phones from LG, one from HTC and, unsurprisingly, Google's own line of Nexus products. Google promised "more coming soon," but even now that still covers millions upon millions of devices already in consumers' hands.

This also shouldn't come as a huge surprise. Remember, last December we highlighted new code in an Android update that hinted full-screen mirroring might be on its way. But until now, we hadn't received official confirmation as such.

Chromecast is already dominating

That's also not to say Chromecast isn't doing just fine as it is. In fact, Chandra also stated last week, "We've sold millions of [Chromecast] devices, and consistently outsell all other streaming devices combined at major retail channels [...]." And that seems fair enough; At $35, Chromecast certainly isn't subject to the same purchasing scrutiny as Apple's $99 set top box.





So why is full-display mirroring, in particular, such a big deal? In short, despite Chromecast steadily closing the gap between itself and Apple TV by adding waves of new supported apps, skeptics still insisted it simply couldn't replace the more comprehensive Apple TV. One of the central points of that argument stood Apple TV's own AirPlay mirroring solution, primarily because it opens up an entirely different realm of possibilities outside the usual media streaming suspects. It's unsurprising then, that AirPlay is often so prominently featured in Apple's marketing for Apple TV.

Apple could still fight back

Of course, Apple might also have something coming down the pipe to improve Apple TV's value proposition. Senior VP Eddy Cue did, after all, recently state the folks in Cupertino right now have "the best product pipeline that I've seen in my 25 years at Apple." So it's reasonable to expect that pipeline should extend beyond Apple's core mobile products and further into the living room.

But for now, when Google finally does roll out mirroring for Chromecast later this summer, I think the affordable streaming stick will arguably represent Apple TV's single greatest threat so far.