dClbydalpha - that is my point, you have replaced a well functioning mechanical system (TR drive failures are rare) with an electric one which is just as likely to fail, so what is the advantage?
Petit plateau - but how much do the TESLA batteries weigh?
My understanding is that the original poster is proposing an electrical transmission for the tail rotor rather than the existing conventional transmission, i.e. no batteries involved. To do this one would need to have the corresponding increase in generation, which crudely will be approximately equal in weight to the motor (assuming that the existing generator is operating near its design limit and so does not have the requisite spare capacity). So that would be (say) 70lbs for (a 150hp generator + a 150hp motor). Still a long way different than the objection raised of 2000 lbs for 150 hp system.
You can go further and propose to relocate the prime mover to wherever is convenient in the aircraft (i.e. low rather than high, or whatever) and put an electric drive on the main rotor(s) with an electrical transmission. Sort of the helicopter equivalent of a diesel-electric ship main propulsion, for much the same reasons. As a further refinement you then only need to put a few small/light batteries in the system and you can run the prime mover over a much narrower rpm band and still handle transient peak power loads; such a system typically has a better fuel economy. Taking an approach like this might be interesting if folk are having problems designing gearboxes, which I understand they are. Tilt wing transmissions are also complex and heavy and have awkward failure modes.
This is an interesting time to be a designer.