Similar like the chrome extension, just show how much unread items there are, and when clicked, open the old reader page
Please see http://theoldreader.com/pages/community
Lazare Inepologlou commented
I agree, but with Opera moving to webkit, perhaps this should wait?
Jarek Malarczyk commented
A speed dial extension might be a better idea, like this one for Google Reader https://addons.opera.com/pl/extensions/details/google-reader-on-speeddial-2/?display=en
It wouldn't even be very hard to do, the counter.json file used in the current Chrome and Safari extension would only need to include Folder names.