I tried creating a Label field type but from the errors I was getting, it doesn’t seem like this is possible the way field types are coded currently and the settings they are expecting.
It would basically just be the title and note field. There would be no editable field on the publish/edit page. The idea would be that you can add additional text/notes to your publish/edit pages that aren’t tied to a specific field. ie. general guidelines for that channel, etc. Plus since it’s a field, you could use Form Layouts to add a new tab, say “Notes” and add instructions in that new tab.