How do I implement Entity Reference Behaviour Plugins?
Answer on IRC via berdir: &quot;no, that doesn't exist&quot;. So it simply does not exist yet in D8.
Supplementary info provided for field settings in D8 =&gt;
berdir:

note that fields, like all config entities have a concept of third party settings. you can use that to store per-field settings. didn't check the other parts
see https://www.drupal.org/project/allowed_formats for a projects that uses third party settings on fields