It's downright dangerous. People are bound to get the indicator switch mixed up with the wipers and end up with soap suds in their eyes and a wiper up the nostril.
If a people wear them on a group ride and go two abreast, aeroplanes are bound to mistake them for a landing strip, and there lies madness.
Reversing bleepers, that's what we really need on bikes, complete with the robotic voice that tells everyone to get out of the way "warning, this vehicle IS reversing" no ifs, buts, safety checks or maybes.