It's not complicated… 

a. Limit e-bike speed to 15mph.  (people ride regular bikes over 20mph all the time on trails which is just as risky,)

or  

b.  Allow only those with a handicapped tag to use e-bikes on trails like auto's have for parking.

Hard to oppose an e-biker using the trail hauling bags of groceries home or hauling work tools. Seem like a real "green" thing that should be encouraged.