I'm so glad to see this effort taking off. Don't forget we have a collection of feature requests for the Content Lister here:
https://www.mobileread.com/forums/showthread.php?t=30379
Regarding having multiple files open at once, I need to be able to do this in class when I'm taking notes (using Notes) and referring to readings in PDF articles. It would also be nice to be able to read an article and take notes in a split window, so a two-screen split would be handy. (Sometimes I want to take notes on the article, but sometimes it's better to take them separately so they are all in one place.)
I'm also really hoping for all the various iPDF versions to be consolidated, but that's a post for another thread, I guess.