I've been wondering how easy it would be to do this with phones.

I've seen documents for setting up wifi networking for a stadium to serve 20000 people. After that you need to know where each phone is. You'd have everyone go to a webpage, with some cameras maybe you could flash the phones in different colors, patterns and figure out where they all are? Or you could just ask users to enter their seat number.

Then download a JS demo to the phone, tell the phone which pixel of the demo to show, make sure the clocks are synced. Instant giant screen!

Anyone want to work on this with me? Getting someone to wire the stadium for 20k people though, and testing it is the hard part?