NSFW Flagging might be the feature of Ello I a most looking forward to seeing implemented.
From Ello's WTF Policies page:
"Don’t post sexually explicit content without flagging your profile Not Suitable for Work (NSFW). NSFW flagging in is development. This policy will go into effect as soon flagging is completed. We respect the diverse views of the Ello community. Not everyone wants to see sexually explicit content. If you regularly post this sort of content, please respect those in our community who do not wish to see it by flagging your profile NSFW."