This issue seems overblown, and I'm not surprised. Child porn is a great trigger word for making people approach an issue emotionally. I'd like to challenge everyone to take a few steps back and look at it more rationally instead. Many people who are concerned about their own instances probably does not have to worry [1]. I disagree with anyone taking the moral high road here too - I think it's disingenuous to call this "child porn" and illicit all of the emotional hatred that it implies when no children are being abused and it's legal to create, posess, and distribute in many countries.
The issue at hand is simply that it doesn't make sense for Mastodon to mirror content posted from other instances. It could be CP, or it could be a copyrighted work, doesn't matter. While this is clearly an issue to be resolved, it's been overhyped and a resolution is underway. I think any court would be friendly to a defendant who mirrored illegal content unintentionally through the behavior of their software in the meantime.
[1] https://en.wikipedia.org/wiki/Legal_status_of_drawn_pornogra...