The plus tire concept has been adopted by most of the big companies pushing e mtbs for at least one model at this point with more to follow I'm sure.
If you are serious about converting to plus size you have to buy rims and tires, but if you just want better traction and small bump compliance you can just get a set of wider 35mm rims of your current wheel size and use your same tires at a lower psi. I did this, run 2.2 tires and have been running at 15psi for 2 years now which greatly enhances traction, small bump compliance and flotation through sand traps. Wide tires on wide rims at low pressures result in to much self steering effect for me.
Granted this is not on an e bike but the same theory should apply.