I can appreciate that folks are pushing to dump Mendeley, especially as a citation manger for private databases. Other than rebelling against the near monopoly practices of Elsevier as a reason, better options exist (e.g. Bookends on Mac or Zotero perhaps or JabRef as cross-platform).
One key reason I use Mendeley is to share journal articles and the notes that I make on those journal articles with my research group. They all decidedly do not have (and even prefer to avoid) Macs. Zotero is not well structured for the PDF purists in the hard science/engineering field. Also, as an early adopter to Mendeley, I have 5GB storage rather than its now standard 2GB. I would hold that no other citation management app is close to what Mendeley can offer for cloud based sharing.
I am transitioning out of using Mendeley (to Bookends) to do my own personal libraries. The data encryption is one new reason. Its slow, cumbersome desktop UI and lackadaisical iPad app are the main reasons.
Would that Papers would be further along in its cross platform, non-Web version release. After being enamored some time ago using it on the Mac, I’ve since given up on it. But, I might predict that when they would get their act together and would offer a well-designed cross-platform app, the ReadCube/Papers team could have a gold mine.