I'll just repeat what I've been saying on the topic.
Based on the tech, streaming 4 uScreens was never the problem, as the tech is designed to send the exact same signal out to up to 6 screens at once, so that is obviously not the problem.
The problem is that they need to figure out how to send different video streams out to 5 different devices all at once.
So really all the GPU would have to do is render 2 different screens at once to support 4 uScreens. Two 1080p signals; One for the TV and One split into 4 section (think 4 player split screen - 4x540p) for the controllers.
The real issue is having a device that can send those 4 split screens out to 4 separate devices all at once. So I agree that yes it comes down to the AMD WirelessTV tech since Eyefinity already has multi-screened display taken care of.
I hope the streaming transmitters aren't expensive, just in case it comes down to them having to include one per extra controller they want to support.