A general description of the proposed change and reasoning behind it is on GitHub: https://github.com/LemmyNet/lemmy/issues/3697
Linear execution of these massive changes to votes/comments/posts with concurrency awareness. Also adds a layer of social awareness, the impact on a community when a bunch of content is black-holed.
An entire site federation delete / dead server - also would fall under this umbrella of mass data change with a potential for new content ownership/etc.
I did perform some tests yesterday. DeleteAccount does NOT Delete the communities created by the account. If the account deleted was the moderator, the community will be left with zero moderators. That person’s post and comments are overwritten, but a post created in the community by an account other than the deleted one should still function (not sure how deep the testing went on that, still enhancing testing).