An option to have the sidebar on the right side would is something I'm very surprised isn't already a feature. It wouldn't require much work to do, and makes morse sense in my opinion. Many websites use a sidebar navigation and when you have any of the messaging apps open it covers that navigation.
It would be the exact same sidebar, nothing else changed but the side of the browser window that it resides in.
Seen MANY people request this, but there is no open suggestion/feature request thread about it and I think we should keep this going, show the opera team it's something a lot of people want.