Hardly. Your assessment that Wifi is too slow is what I called out because numerous apps on numerous platforms already do what you said wasn't possible. I stream over wifi with PLEX to the Roku everyday. With a little bit of hunting I found "Juice" for Roku that sounds like it will do a great deal of what Airplay does by allowing you mirror many apps on Android to a Roku box.
But again, my comments were not directed specifically at finding a mirroring app for Roku, instead just to make sure that the community knew that you indeed COULD stream over wifi. A streamed screen content would be no different than streaming an HD movie.