Feature Idea (one per thread):
Currently if you need to create an entry for a specific content relationship or linked document field you need to first create that entry type go to the content type you would like to link to it and then link it using the Link field or Content Relationship field. Ideally if a linked doc doesn't exist it should be simple to just create a new entry using your desired entry type, or if it is a specific content relationship field then any new entry of the types allowed via that content relationship.
Issue that it solves:
Reduces the content editor having to go between different content types to produce content.
Screenshot or video of the issue (if applicable):
You could have a button (highlighted in red) in which the user can create a new content entry of X type.