Could there be collaborative moderation where node admins volontarily block other nodes or onion services that host CSAM?
I wonder if that's technically possible for a hidden service directory or rendez-vous point to do that. It wouldn't completely kill those services, but may at least make less Tor resources available to them.
The trickiest question may not be technical but organisational. The Tor project probably doesn't want to be in a position to validate/decide block requests. Different entities all over the world would ask for blocks, for many different kind of contents.