This 'followers-only dogpiling' issue has been around for a long time. It is a major reason given for why some people, particularly Black people, have abandoned Mastodon. It seems like something that would benefit from soliciting user input first. This would have the advantage of really defining the mechanism of abuse, raising awareness that it is an issue the Mastodon cares about, and achieving buy-in to proposed resolutions.
cc: @mekkaokereke