Somebody, called Kensuke, enabled Mircast (Streaming screen over WiFi) for the Nexus 7. I don't have mine here so I can't test it.
Maybe somebody can try it out.
It seems that he compiled the complete 4.2.2 ROMs with the addional Miracast Support.
Try it on your own Risk!
Credits all to Kensuke!
His HP: http://d.hatena.ne.jp/RC3/