E-bikes are sick and look like a lot of fun (I want a Turbo Levo).. but in the right place. I do not like the idea of people riding there e-bikes on MTB trail for one reason, most MTB specific trails are there because a local group worked very closely with their local government to get permits to build trails and these permits (atleast in TX??) specifically state no motorized vehicles. E-bikes are definitely a grey area currently and here is the issue: MTB trail can get pretty gnarly and there are risks no matter what, but for the most part your fitness is a huge limiting factor on how fast you can ride the trail. As you your skill rises from riding a lot, your fitness does too. It goes hand and hand. The E-bike takes fitness out of the equation, so all the sudden you have random Joe pushing 20+ MPH through trail that is not designed to be ridden at those speeds (unless you are a highly skilled and fit MTBer). With most Government ordinances already leaning away from the risks involved with having a public mtb trail, and equestrians/hikers fighting for the same cut of land, we are 1 lawsuit away from having MTB trails shut down..
I do think it would be sick to rip mtb trail on an e-bike, but I would know what I'm doing.. when to push, when to chill, you get the idea. Unfortunately we will be the minority and the weekend warrior type guy will be the one that's riding too fast, gets critically injured, and then sues.. potentially ruining it for all of us.
E-bikes are sweet and will have a place in the sport, but finding that place is going to be the challenge over the next few years while they start to become more popular.