Wow, pretty nice! 
What’s your opinion on reading papers as PDFs vs HTMLs? I see how PDF feels more like something because it’s a file that can be downloaded, saved locally, forwarded via email etc, compared to just a link.
However, “philosophically speaking”, I would like to see more of a world in which research is published online, optimized for digital reading (two column pdfs just make me sick), with a version history, interactive figures, embedded code and more!
Instead of everyone downloading PDFs, you could highlight directly in the HTML using for example weavatools.com to grow your library, with local notes that directly link to the online version of papers / articles / all sorts of web content.