If this is a thing, and I'm not saying I'm participating even if it is, the rules/parameters for the cars need to be decided and agreed upon. This needs to happen soon, so those building cars can build and NOT have to change what they're doing to adapt to new rules. Wheel size, attachment points(wheels first, or behind front of valve cover? Inside or outside of cover?). Final max weight? Height, length, etc.
The length of the track matters, and quite honestly a 5 pound car can be moving very quickly at the bottom of the proposed hill and quite probably hurt someone. There needs to be a plan to stop these things that doesn't involve someone trying to catch them. Gravity, you know, it's a thing.