No e- mountain bikes here where I ride in the Midwest. Not to say they don't exist, but I haven't seen any on the trails yet.
I'm not really a fan of seeing them on the trails either especially if the people riding them are perfectly capable of pedaling a bike.
If one is inclined to go to the bike park and all they like to do is the "downhill thing" like skiers I can kinda a see a purpose for them to pedal back to the top. Saves the legs and the cost of a shuttle service.