Weight really isn't such an issue with ebikes. I'm riding around a 62lb clunker, carry a 10lb chain lock everywhere, plus I'm hauling big loads of groceries and other crap. Even an extra 5lbs isn't going to make a big difference, nor would an extra $150 to the purchase price if it means years of added longevity.

The engineering challenges make sense. Hopefully it is something that is being actively R&D'd.