I've seen somebody setup the AppRadio like this:

Equipment:

*) AppRadio in car

*) AppleTV in car

*) AirPort Express (or cheaper wifi access point) in car

Setup:

*) AppleTV is connected using HDMI to AppRadio.

*) iOS device (iPhone/iPad) is connected to AppleTV using AirPlay for wireless audio/video streaming.

The above definitely works and I've seen videos of it.  However, does the AppRadio touch screen still work?  I think that it should because the touch control uses bluetooth which should still work!

What this setup would allow is wireless HD audio/video from the iPhone and you wouldn't have to connect any cables to the phone or anything like that.  For example, the passenger could play games on the phone and no longer be tethered to a cord, etc.  (or you can keep your phone in your pocket, etc, etc!)

Does anybody have the equipment want to try this out?  I'd love to know if it works...

It should, however, the boot up time would be both incredibly annoying, and it would be most likely unreliable. Also you would be throwing in another area of lag on top of artifacting issues. However, yes this should work. The AppRadio has no clue what phone or device is connected to the HDMI port, only that something is connected. The controls go through bluetooth and that's how the device manipulates what's on screen. Again though, you're looking at more lag, data connection issues, increased time for the router to boot on a cold start, and then for the iPhone to pair to it, and then you have the issue that using this setup you will have no internet access using the phone's own connection. 

To answer your question yes it does work.  Let me explain to you how I have it done in my vehicle.

1st I drive a Chevy Colorado.  I have the AppRadio 2 installed with bypass relay and whatnot. 

I have a HDMI cable running from the back ofthe Appradio Headunit to my glovebox into the Apple TV.

I have a power inverter inside the glovebox as well powering the Apple TV.

The Airplay you have a few options:

1.  If your phone is jailbroken you can throw mywi app on it on infastructure mode and connect the Apple TV to the wifi from your phone and send video and audio via wireless that way

2. If it is not jailbroken you will have to have some type of wireless in your vehicle.  One of the best options is to use a wifi hotspot device (say from AT&T) and connect both your phone and Apple TV to it that will not only feed your video and audio to Airplay but will also supply the internet data as well.

Remember if you hide the Apple TV in your glove box the remote with your Apple TV wont do anything unless the glove box is open and remote is pointed to it.  I like to use the Apple Remote app from my phone to control the Apple TV.

Im able to feed video and audio as well as Airplay Mirroring.  Although no touchscreen support is there it still fits my needs as I have my phone docked close by.  Any Questions feel free to ask!