actually the idea has been around for a long time for large diesels and i forget who the big guinea pig was for a manufacturer... but it is pretty simple idea...just the cost of all of it.
it would involve solenoid actuators pushing the valves open against the spring force..and of course all the solenoids would be timed and controlled by a computer sensing the speed + crank location + desired speed/output. it could get complicated though and what would happen if one of the solenoids failed!?? it all involves very fine timing of not just how much the valve opens but the rate too...it HAS to be mainly linear to the RPMS like a cam does it. you could have unlimited VTEC LOL!
the advantage..probably not a big weight savings but a considerable increase in HP/TQ because of less rotating mass, friction, etc- follow? i guess the costs outweigh the benefits and thats why we have cams.