I added my name though the sign-up form, but I would love to see the Android beta sooner rather than later. I was one of the original PaperPile beta testers, and it is absolutely incredible how far the app has come. I switched from the "Papers" program on the Mac when I joined the beta, and never looked back. Four years of doctoral study, and PaperPile has never let me down. I just wish Academe (and publishers) would drop the love affair with Word and use Google Docs and LaTeX (depending on whether math is needed) instead.
My biggest use for PaperPile on Android would be to quickly look up references on my Nexus 6P phone, when it is not convenient to get out my computer. This would mostly require searching the metadata in my library; searching the PDFs would be helpful but not as important. I would need to browse the PDFs as part of that functionality, but not read them in a serious way.
My second use would be reading papers for-real (and annotating them, if possible) on my Nexus 10 tablet, on the occasions when I don't feel like using a laptop or Chromebook.