There have been devices that downloaded data by pointing a photoreceptor to a screen and blinking like mad.
Two parts to think about. Can HTML5 blink an element fast enough. What would the receive circuitry look like.
Say for example, this http://www.wayneandlayne.com/blinky_programmer/
So, defiantly doable.
My quick cute idea to just blink out the same manchester encoded data that goes into the Audioino stream suffers from a data rate issue. I gave up waiting, went and exchanged some coffee, and it was still blinking away.
Need to figure out what kinds of speed limits are in this method; might not be usable because of this.
Exploring issue #6 trying things out.