I honestly never considered powered bikes as anything but a motorcycle alternative. they got nothing to do with bicycles and I don't care about their potential demise (which is kinda overdramatic, that is nowhere on the horizon).
I know I have nothing but disdain and resentment when they hug bike paths, sidewalks, etc. and in my view those things should be in regular traffic lanes, same as mopeds and motorcycles.
as to the combustion part, no idea how prevalent that is but I wouldn't keep this thing in my home or near it.