I think rather than having a playground, you should just put some sample nodes / lists in the Organizing section that people can delete later if they want to. As an example Notion (https://www.notion.so/) populates your workspace with examples from the start, with mock data filled in. That way you can click around with existing data, see how it works, and delete it if you don't want it.

I'm trying to see how the memorize function works and because I have no entries in Organising it won't work. I see there's examples in Playground but I can't see what they look like when trying to Memorize. I spent a few minutes trying to work out if it's possible which was pretty frustrating, and it looks like it isn't, and if it is possible then I have no idea how to do it. Having to invest time into creating realistic mock questions is a pain when there are some right there but just out of reach. The Playground is essentially just Workflowy and doesn't let you experience the rest of the app, it's not a good experience.

That being said, I really like this idea as this reflects how I used to organise a lot of my notes. I'll definitely give it a shot and look forward to see how it progresses.