Good idea - does it work? Aren't there IR filters on the lenses? Either way it won't stop the idiots though. People are so used to being removed from the experience and seeing it through a 4" screen that they stand at the front and ruin the original experience for everyone else. It's a real real problem for artists.
Crappy shaky mobile footage is horrible to watch and sounds dreadful, but worse than that, it beaks the artists connection with the audience. They need that connection in order to give you a good show and put their best out.
Irony is many concerts or tours are filmed for TV/DVD and the quality difference from having a professionally filmed 20 camera, brilliant angles, brilliant audio production vs mobile phone is complete. Yet those mobiles detract from the proper production with the horrid wall of white rectangles (some even in portrait ffs).