Where I ride (and I would guess like most places) there's not enough forest ranger/park ranger coverage to address this in any effective way. Maybe if they can catch people when they're coming off the trail back to their vehicle.
I ride a class 1 eMTB (not modified.) in my experience, downhill is EXACTLY the same as an unpowered MTB - for the most part, the motor is doing very little work. Climbing is where the difference exists. For myself, I find my climbing speed boosted by perhaps 3-5mph; it's noticeable but it's not excessive imho.
That said, I also don't do stupid shit. I don't climb one-way downhill trails. I don't ride outside of my ability to stop/avoid - ie bombing blind turns. That's all my own choice though, there's no one enforcing it aside from other bikers. I've encountered hikers climbing trails ignoring one-way signs, people are just fucking stupid sometimes.