Do you really think so? This really just brings national parks into alignment with most other areas I've traveled, and I'd be surprised if there were hoards of e-bike riders in the area holding themselves back from riding on the canal trail because of the previous rule. I just rode from Pittsburgh to DC this spring. The GAP section, I assume, had no ban on ebikes, but if there were any ebikes sharing the trail with me over the course of the week, I didn't notice them.
Last fall I rode the Katy Trail, or part of it at least, and I did see a few ebikes. They were touring the trail as well, not "day riders," if that matters. One of them was one of my traveling companions, my uncle who had ridden the GAP with us the year before, but found it very taxing given his age and some recent heart issues. And then there was a father/daughter pair who stayed at many of the same places as us along the way. They both appeared to have reached retirement age, at least the father had. I only noticed they had ebikes because we shared a shuttle with them. Rode a stretch of the Erie Canal trail last month again with my uncle on his ebike. I didn't notice another ebike the entire trip, although we did run into one cyclist going the other way who stopped to grouse about a group of "cheaters on ebikes" he had passed earlier in the day. Why it ruffled his feathers how someone else traveled, I don't know. Why he had to share his displeasure with my 70 year old uncle who would not be able to travel with us if not for his ebike, I really don't know.

I ride all the time on trails where ebikes are perfectly legal, and I still hardly ever see them. When I so see them, I don't see how they are using the trail any differently than any other bike rider. Trail impact seems the same as another bike, so this makes sense to me. It also makes sense, if you want public support for these spaces, to make them as open to as much of the public as reasonable.