I’m not sure it would be much harder to regulate than Themeforest. After all we’re already selling code, even if it’s html and javascript code. You just have to trust people.
Here’s an idea that could also apply to Themeforest: the big problem with free scripts is lack of support. How about once you’ve bought a CodeCave script, you have access to a private support forum for that item ? This way people who pirate the script would be missing out on a lot more.