So from the biggest issue being "awareness for bikers", you have decided that bikers should do more! This obviously means more expense for us. Plus it will then probably be made compulsory, be part of the MOT and we would get points if the batteries ran out part way through a ride for "failure to comply".
I do not consider it being a good idea, whether it was retro or designed in. I have seen these on cyclists helmets.
A retro fit would have to not disturb the integrity of the helmet. Not really an engineering project. Easily knocked up with a medium set of Meccano or Lego Tecnik. Also, one of the beauty's of expensive helmets is that they are light. Not sure what a battery pack would do for that feature. If the answer to drivers being more aware of bikers is lights, then add the lights to the bike. This solves the majority of issues with a helmet light!
Give everyone involved in an accident a minimum of 3 points and £100 fine, this would also help the economy.
Can you design a bikers disintegration ray gun to blast anyone who pulls out on us?