Turning crowd's [smart]phones into pixels

I was wondering today about a video i saw recently about an interactivity company (YDreams), in which an outdoor crowd would control "the spaceship" on an Arkanoid style game projected on a very large outdoor display, by waving a rod left and right.

I was probably looking at my phone, when i thought about a similar project except that an application that people would install on their phones, would allow them to be controlled by a central server, basically turning them into pixels, allowing for video/visualizations to be "projected over the crowd".

Given a large enough crowd, as "aligned" as possible, it could be really an awesome experience.

What do you think?