For those who would like to test it, i put up a demo catalog (with some public domain books) here :
http://cops-demo.slucas.fr/feed.php
Please tell if it works or not especially if you're not using FBReader or Aldiko (I already know these two are working fine).
You have to use an OPDS client to check the demo (a normal browser or feed reader won't do). A list of OPDS client is here :
https://wiki.mobileread.com/wiki/OPDS