The pessimistic hat is a handy hat to have around!
If there was one interactive playground website, I would imagine it to have the “most common use case scenarios” – a couple of menus, blog posts, categories, tags, a handful of pages etc. I think this would help beginners get off the ground. Then (blue sky hat on), when a user interacts with the playground website, a new instance of it is spun up just for that user.
Why does my example menu work in the playground but not on my site?
This question is much easier to answer if you actually have a working playground you can play with and break yourself.
All big conjecture but I do like the idea!