It would be extremely valuable if Paperpile had an associated mind mapping too (also referred to as concept mapping) that allowed you to link related references and annotations. This tool would ideally have similar functionality to tools like the opensource Freemind or Coggle.it but would link back to original reference or annotation in Paper pile. It would be nice if it could also export as PNG, PDF, HTML, or text form in outline format.
This has been suggested before. We don’t have plans to add mind mapping features. We want to concentrate on the core functionality and not get distracted by features that are better implemented in dedicated software.
I had a look at the open source mind mapping solutions you have given above. My suggestion is to link from a web based mind mapping solution (could based) like creately. Then you can directly embed the diagram in to the workspace. Here are some Mind Map Examples from the diagram community of above mentioned.