Earlier quoted context omitted.
Opera isn't switching to WebKit, it's switching to the Chromium codebase (which uses WebKit). Chromium is a full browser, so Opera is basically outsourcing it's browser development to Google (which aside from practically all Chromium work also does most WebKit work these days). This makes perfect business sense for Opera - why work hard to make a browser, when it can get one for free. As a plus, that browser uses Web…
What makes you think Opera is outsourcing development to Google? Just because something is using a framework doesn't mean they aren't using it to build their own thing on top of it. Your comment doesn't make sense. It's wild speculation based on an article with false statements.
They are using Chromium as their browser. Chromium is a full browser, so basically almost all the work on Opera's new browser will be done by Google. That is why I said "outsourcing development to Google", but of course I didn't mean it literally as in "paying Google to develop for them".
That's not speculation, that's just what it means when Opera is switching to Chromium.
Opera will add stuff on top. But Opera can't differentiate much in the core browser stuff, otherwise it would be forking Chromium and it would become harder and harder over time to get updates from upstream. That makes no sense technically or business-wise. What does make sense is to add things on top that are modular and separate, for example remove Google's login and replace it with Opera's, etc.