Stefan, thanks for being candid about no concrete plans to add offline functionality. Offline support although I use rarely, i.e., poor wifi reception, traveling, conferences, hotels, it become crucial for those times when I need to look up into paperpile and there is no Internet. I am currently on paperpile trial and contemplating to give up
zotero + box webdav for storage which I love most. As some of users mentioned, browsing through pile of pdfs, either cached or stored on drive does not help without standard web interface of paperpile which gives awesome annotation functionality for linux users. That is the principle reason I switched from zotero to paperpile as on-the-fly pdf annotations for linux user is still a big issue for zotero. So, I may end up keeping both zotero and paperpile for while and hopefully, at some point give up my obsession for offline mode.