But it must breach the laws of the game because no camera could be made of a sufficiently soft material (I assume) for it to pass muster:
Law 4.4(c): A player must not wear any items containing buckles, clips, rings, hinges, zippers, screws,
bolts or
rigid material or projection not otherwise permitted under this Law.
(g) A player must not wear any other item which does not conform with the IRB Specifications
for such clothing (Regulation 12)
Reg 12:
(g) Headgear*
A player may wear headgear made of
soft and
thin materials provided that
no part of the headgear is thicker than 1cm when uncompressed and
no
part of the headgear has a density of more than 45 kilograms per cubic
metre.
http://www.irbplayerwelfare.com/?documentid=52
This thread will, no doubt, lead to an investigation by the QRU - before you know it players will be wearing headgear with earpieces so the coach (or others) can give them instructions in real time: that would be a shit house development.