We've decided the benefits to T178842: If a user has never triggered a logged action on a wiki, they should not be able receive emails by non-privileged users from there are minimal and the drawbacks are too complex to address individually so we will rollback T178842.
This form of harassment can be addressed in T16950: [Epic] Support global preferences on Wikimedia wikis
But I'll state here yet again that I think we can find more intuitive ways for users to be proactive about their email correspondence.
Clean up/get rid of the code too, we won't be coming back to this concept.