I used a homemade cart/5 gallon can contraption to hike in the desert around Death, Eureka and the Saline Valleys many years ago, but I don't think this is the intent of the proposed law. More likely, it's a "foot in the door". After all, abandoned strip mines would make great mountain bike terrain.

I was run into on a trail on a Isle au Haut in Maine. It's part of Acadia National Park. Put a pretty good cut in my leg and luckily my FAK covered the damage. I had no choice , but use a trail that was multi-purpose at the time. Now, the NPS discourages mountain bike use on the island and their use is banned on hiking trails. Dual use of foot oriented trails is a poor choice for both users safety and enjoyment.. I know of one place in the Smokies where carts are popular to bring gear up Hazel Creek, once they are ferried across Fontana Lake. It can get very crowded, as the carts allow for "bringing the kitchen sink".