You might see that the Dropbox Community team have been busy working on some major updates to the Community itself! So, here is some info on what’s changed, what’s staying the same and what you can expect from the Dropbox Community overall.
Status:
Closed
Allow Users to Leave a Shared Dropbox Paper Document
Currently when a Dropbox Paper document is shared with you it's impossibe to remove yourself from it. Not only this, but all others that the document has been shared with can see your email address. ...
Actually, looking at the listed of declined features in dropbox paper is a great list of feature ideas for someone else looking to build a competitor to dropbox paper.
https://www.dropboxforum.com/t5/Dropbox-Paper-ideas/idb-p/101002012/status-key/declined
After all, most are features asked for by several people - and given how difficult it is to find this, that's a good indication of how much people care.
Been thinking about making a pet project and dropbox paper would not be particularly difficult to replicate...