Regarding illegal (moped) E bikes that do not fit the current class 1,2,3 E bike classification system, it is pretty simple, they are legally a moped and require license, registration and insurance to be used on public roadways and have no place on city bike paths or mtn bike trail systems. People who choose to build a DIY kit bike that exceeds the 3 class system or deregulate their brand name E bike in order to have a faster more powerful E bike are knowingly altering their E bike into a moped. From a law enforcement view, yes it is a problem, just like all the people who swap out their headlights in their car/truck and install illegal ultra bright headlights that blind oncoming traffic, or the Harley and UTV owners who replace their stock exhaust with loud after market pipes in violation of city decibel sound limits or any other number of similar examples.
Ultimately, these type of issues get sorted out in the Courts when there are accidents and lawsuits. Frankly, I am amazed that people are using these non classified vehicles without worrying about what will happen when they accidentally run over a pedestrian or get hit by a car in an intersection. In the US, where lawsuits are a way of life for many people and you stand the chance to "lose the farm" if a judge decides you are in fault because at the time of the accident, you were driving an uninsured, unlicensed and unregistered moped, even though you were following the other traffic laws and were not at fault otherwise. That is way to much risk for me to want to modify my new E bike, void the warranty and potentially lose my life savings just to gain some power.
I can offer one answer on "how do you determine the class of an E bike"? I think it might come down to some stickers/badges/plates (?) and some new laws about misuse of displaying these "plates". Manufacturers can install a permanent badge onto the motor/hub of an E bike that displays the class and power. DIY kits are required to comply with the laws if they sell a legal class 1,2,3 kit and the kit includes a badge that shows the class of the motor. DIY kits that exceed the power of class 1,2,3 have a "branding" that shows class non compliance (moped) so LE can easily ID the vehicle when they are involved in an accident or rangers patrolling trails. Probably some laws specific to Ebike and mopeds about misuse of plates, so it can be sorted out easily when there is an accident. It will take some time, we are talking about a whole new class and style of vehicles to integrate onto roadways and trail systems, there will be accidents with personal and property damage. Sooner we figure it out, the better for all.
As far as being able to use a class 1 (or 2/3) bike on Public Land existing bike trail systems, I would have no problem going to local BLM or FS office to get for free, or even pay $20, for an permanent or annual sticker to be put on my bike that allows me access to public land bike trail systems so I could share bike trails with other pedal bikers. This would also be a good time for the land management agencies to do some education and go over the expected trail rules and etiquette to help the different user groups be able to best share the trail system without conflict. I think it will come down to the E bike owner swearing under oath their bike is to best of their knowledge unaltered and is a class X Ebike as designed by the OEM manufacturer or has been built or altered to comply as a class 1,2 or 3 E bike. You lie under oath and get into trouble due to "excessive speed" as determined by LE, it comes back to bite you later.
The class system is not without issues and problems, but at this time, it seems like a good way to sort out the E bikes from the mopeds and hopefully that will help get more single track trails and city bike paths open to E bikes. I have a LE background, can you tell, haha?