One of the biggest reasons internally geared hubs fail on motor assisted bicycles is due to how they are used. Many internally geared hubs don't like to be shifted while peddling. I am a bicycle mechanic and I have rebuilt my fair share of internally geared hubs. Shimano and Sturmey Archer hubs can be damaged if they are shifted while the pedals are turning, even if there is no load. With a shift kit installed, even though the pedals are attached to a freewheel bearing and remain in the same position, the bottom bracket and the drive chain going to the internally geared hub could still be spinning.
I burned through a half dozen internally geared hubs before I found the SRAM G8. It can be shifted while the drive chain is spinning, but like any bicycle shifting, it should be shifted when not under a load. For my bike, I just let off the throttle, shift, then back on the throttle.
I have the disc brake version of the G8 and it has been a very solid hub.
All this said, SRAM has discontinued all production of internally geared hubs as of FEB of this year. That means parts are going to be hard to come by in the future. But, if you can get one off Ebay or Craigslist, I highly recommend the SRAM G8 disc hub.