Chromecast-like function on MacOS over AirPlay

This is kind of a question on AirPlay for devs out there.

In the Chromecast review, Nilay Patel says:

[Chromecast] is the first device that's made it easy and desirable to put browser on TV.

And I was wondering why not AirPlay? It has enabled screen mirroring onto TV from MacBooks for years.

To that, Nilay replies, "Chromecast is better for watching web content like that — you don’t have to mirror your entire screen, you don’t end up changing display resolutions, you don’t end up sending system audio along with your show, and you can switch apps and do other things while the video plays."

I see the point with this, and am wondering if there's any Safari extension that turns AirPlay into something like Chromecast, or if that's even possible. If this can be done, then AirPlay has huge edge over Chromecast.