I'm not aware of any instances of this but the solution is pretty simple. It's not dis similar at all to the current web. At the end of the day, any node that faces the public is a web server that is serving content, whether it's backed by a Blockchain or not. If it transmits a mentioned "illegal content" then it must cease to do so just like any other web server.

What is the practical solution? Clean nodes. If such web server is in a jurisdiction of said illegal content, it must run a clean node that specifically filters such content to the web. This technology exists today, it's called "moderation", it's just that the backend is a MySQL database, not a blockchain.