Endurance-Series will never become electric.
Though, e-Power isn't that green at all. Just do a little research what chemicals and other enviromental poison are used to build the batteries for that cars. Still, there's another problem: The durability of the batteries. The amount of possible loading-capacity will decrease a few percent every time you go recharge it. It will only become popular a few decades, before poeple get to know about the problems. I can imagine, how expensive it would be to get a new battery in it or to expose it after all.
It will be the same way the Diesel is going. Now, everyone gets exited, nobody cares about the problems or will say "Uh, it's just a matter of time to get rid of the problems". Nope, it would not. In 40 years, there will be another scandal like the one we have now with Diesel and cartel-agreements. And that would be the end of electric motorsports as well.
Nope of that matters, none of what we mortals think matters, what matters is the car makers making vast amounts of money. If they feel they are simply racing for the sake of it they will leave and go to the place where its relevant to develop tech and brand awareness.
I can't understand how people can be so blinded by their knee jerk reactions to not see how much the motorsport landscape has cahnged over the years and for the most part it just gets a new audience, BTCC used to be better, WTCC used to be better, F1 used to be better (people have been saying it was better before since the first ever season many moons ago most likely).
In fact i'll go further Motorsport is pretty dead on its arse, the club racing scene is dying as well.
It won't take much to transplate it all with electric racing, race trcks will start hosting races and phase out petrol race cars becasue the other issue for race tracks in fact the bigggest one is the noise levels.
None of the people born before 2010 will be happy about this, i'm certainly not, but as a racing fan i'm starting to accept it for what it is enjoy what we have currently as it will be 10-20 years before we see massive changes, but it's coming to and end and the kids born after 2010 will be the new audience and they will know not much different.....
What people really need to stop being so dense about is how raw the first F1 cars were compared to 50 years later, 50 odd years ago they were racing on roads and air fields, now imagine in 50 years time what electric race cars could look and perform like. Short sighted blinkered views on this topic won't help anyone, racing is racing IMO, i can even enjoy the Tour De France and Usian Bolt as i like to see people race, yes the noise of engines turn me on, but if they go then i will still watch racing.... open your minds.