Ok so apparently rolling back the chain in case of a CSAM OP_RETURN is also proposed as an activation mechanism for this “anti-spam” soft fork drafted by @Luke Dashjr @Luke Dashjr.

Also, even if no such OP_RETURN is mined, they want to activate this as a UASF within ~three(!) months.

https://github.com/bitcoin/bips/pull/2017/commits/3c718237072c107ced8c3531a487354fbdae55df