As you already know, concerns have already been raised about the use of e-mtb's at organised mtb sportive events. The most recent being an Evans ride it, where many questions were asked, and many issues raised.
I'm riding another in a weeks time, and it'll be interesting to see how things go with the organisers that day. I'm already expecting the potential for them to refuse my entry, and in reality I can't blame them. One accident and claim involving an e-mtb fitted with a dongle, could pretty much destroy a company, and as they have no way to check/police it, the only option available to them, is to ban all e-mtb's.
I won't argue the case if they so decide to take this action, as I shall just take along the pedal mtb, and reduce the ride length. I shall be deeply disappointed though, that my riding pleasure and the riding pleasure for potentially countless others over time, has been spoilt by a minority through their actions of blatantly flouting the law, which will have caused this chain of events to happen. I'm sure that trail centres will quickly follow suit as well, with even more e-mtb riders then facing disappointment.
I hope that it won't ever come to this, but I'm not going to be surprised if it does.