This is bad news. Another step on the way to browser monoculture, with all the problems that can bring.
"It was always a goal to be compatible with the real web while also supporting and promoting open standards. That turns out to be a bit of a challenge when you are faced with a web that is not as open as one might have wanted."
The web isn't open. It never was. Many, many sites only start working properly in Opera when you mask as IE/Firefox, because browser sniffing is still a thing even in 2013.
The popularity of Webkit also brought its share of problems. Too many blogs and sites raving about experimental features, which end up being used on production sites with no fallbacks.
The majority of Opera users won't care. The rendering engine is highly insignificant; people use Opera because of what the browser as a whole can do. I find it mind-boggling that you still need *extensions* in other browsers for something as basic as mouse gestures. I also have no idea how you can remap keys in Firefox or Chrome. Perhaps an extension as well for something as simple as that? Don't even get me started on UI customization; there's nothing that comes even close to what Opera can do.
Opera was and still is great at innovating. Many "standard" features like tab reordering, speed dials and even ad blocking (!) appeared in Opera first, sometimes half a decade before someone else implemented it. If adopting Webkit means they can spend more time doing that, and if the "Opera experience" still remains, I'm fine with it and couldn't care less.
By the way - Opera's been losing market share to Chrome in countries where it was most popular (former USSR). Now there's no reason for those who switched to continue using Chrome. They can return back to Opera.
What still needs to be explained is what happens to all the embedded systems running Opera. That includes fridges, vending machines, airplane multimedia systems, and even the Wii.