Most trails are built with a directional orientation, and this is usually listed in the Section 57 approval (i.e. downhill primary). I would suggest that the person riding the trail in the primary direction holds the right of way, regardless of their propulsion system.
People that ride ebikes up descents cannot expect others to move for them.....that would be looking for special treatment just for them as any other rider would almost certainly not be riding in that direction. If they want to be classified or treated as a MTB, then they should ride like one at least in terms of the direction they ride the trails. It seems that most people here agree on that point. It's unfortunate that some irresponsible individuals are promoting ebikes by riding them up descents. My main concern from the start was not the technology, but the application.
As a person with zero desire to ride ebikes, and who has generally been pretty crusty about them being given open range, I can cite two excellent examples of ebikes on the trails recently. Last week, I caught up with a group on a climb. One was a woman I hadn't seen on the trails in years. Like a proud vegan she had to inform me that her new bike was an ebike. I said nice paint job. Main thing I noticed was that it was quiet. Second thing was that she was riding with a group of other MTBs at a fine pace. It is possible. Knowing this person, I realize there is no way she would have been out if not for the motor assist. Good on her.
Second example, Search and Rescue had two early responders attend a critical incident tonight by Ebike. It was a very difficult access point, with no other real way of getting in with their packs. The Ebikes were perfect for it.
These are good examples. I remain in favor of responsible integration.