Hopefully this is the right place for this!
First off, amazing app... LOVE IT!
There are a couple things that would pretty much make it the absolute MOST amazing calibre companion ever.
I believe I saw mentioned you were considering cloud connect? Please please please PLEASE do add this! I keep my library on dropbox, and I've been using Calibre Cloud Pro to access it on the go, but it doesn't allow me to search by series, and the book information does not display series numbers that have decimal points, so a book 0.5 or 0.75 (prequels to the series, for example) are displayed with no series number at all, and books 2 and 2.5 are both displayed as Book 2. I read a LOT of books in series, so it gets confusing, and annoying, and reporting this to the dev has gotten no response in months.
Secondly, it would be super nice if you could do, at least, an "open with" type operation when your app option isn't available. A couple things CCpro does right is that it
allows you to click-upload books to google play when they are epubs, and more importantly, click-email mobi books to my kindle email address, which lets me get them into the "amazon clouds" and I can keep my reading progress synced between my Nexus 7, my Moto G phone and my Kindle Paperwhite. (CCPro supposedly will add books to your kindle app without the email, but it's never worked for me so.. meh)
I can obviously do these things manually once I get the books onto my device, it's just a couple neat features that would be cool to see pop up someday
Edited because the google play feature was in there, just a bit harder to find