I have recently become a Perlego subscriber (https://www.perlego.com/ - self-styled as Spotify for books) and I think there is a great opportunity for integrating the services. They have a lot of books that one’s academic institution might not have and it is even more useful for independent researchers without institutional affiliation & access.
While they don’t have a proxy , it would be very useful if at least bibliographical information for books being read by your account in Perlego could be synced with Paperpile including a link to the fulltext and ideally the notes/highlights imported as well. At the very least, Paperpile plugin should be able to read the bibliographical information from a book’s page in Perlego.