Speed limits would likely have as much effect as class restrictions, as only the law abiding would honor either.
Unfortunately speed is only a small part of the issue. I would encourage anyone involved with ebiking to contact their legislators and regulators to find out all the reasoning behind the regulations. Being involved in access issues locally I've found the explanations much more complex than just the speed issue. Some regulators know nothing about ebikes and others know a lot. Then there are some that know nothing and don't even want to learn. We need to be the educators, the ambassadors for ebikes. But going in with an all or nothing attitude won't work because the other side have tax paying citizens too, with the same mindset. They have an easier path to victory. They feel 'we were doing fine without ebikes, keep them banned'. Or, 'this new headache is too much trouble. Ban them all'.
Regulators and legislators have to balance everyone's concerns. It's much easier to work for better and more access from the inside. As for speed limits, I fear most will not be happy when they are enforced. I've seen many trails and paths with speed limits and none have been higher than 15 mph and I've seen limits as low as 9 mph. That wouldn't go over well with acoustic or assisted riders.