I reckon that most people reading this thread have already flown an electric helicopter. I actually owned my own a few years back! Okay, so it was a scale model co-axial helicopter with a little remote control but still it proves it is feasible.
I guess what is needed is a substantial amount of investment from our industry. However, considering a hell of a lot of helicopters are sold to service the oil industry to extract fossil fuels I'm doubtful that helicopter companies will be pouring money into R&D!
As an aside lets hope electric helicopters don't fly into walls like mine seemed to have a habit of doing!!
PT