No, if I can't run it on my machine then it's just an idea. I didn't say it was a simple or obvious idea - I said it's just an idea.
Anybody can make something pretty in Photoshop. If he was serious about getting people to implement his mockup he should have spent a few days writing a quick and dirty implementation, with real code that could be improved upon later.
It's just a chat app. We all know that programming it is feasible because it has been done hundreds of times before. That part isn't interesting.
What's interesting is the interface, which is why we're discussing it. The fact that you can't run an application doesn't make the concept any more or less interesting to discuss and critique. The issues being discussed aren't solved with code.
Anybody can make something pretty in Photoshop. If he was serious about getting people to implement his mockup he should have spent a few days writing a quick and dirty implementation, with real code that could be improved upon later.