You do realize that the aspect ratio of your iPad is 4:3, and the Nexus 10 is 16:10? What exactly is it supposed to mirror if not its own aspect ratio? Video out is app-dependent, so some apps may only support 720p on external HD TV's etc. Playing 1080p video shouldn't be a problem in apps that support it.
I don't expect anything, which is why I'll be pleasantly surprised if they do. If they don't, I will not have been exhausting myself with handwringing while waiting to see what happens at WWDC in a short month from now.