On an electric bike you don't need a Rohloff, though it is a pleasure to have it. An 8 speed Shimano Nexus/Alfine box has all the range you need, because the battery and motor fills in the rest for you. But that applies to a utility bike, or short recreational/exercise rides within reach of a recharging point. If you're touring with an electric bike, as people are now doing in Germany, or you're taking long daysides, you will feel the loss of the Rohloff's range keenly the first time you run out of battery an hour or two from home, all of it uphill of course.
Still, if I didn't have a Rohloff on my electrified bike, I would choose the NuVinci over the Shimano Nexus/Alfine type, of which I have considerable satisfactory experience. Weight is an irrelevance on an electric bike, once you have a big enough battery.
