Opera promises that the change is primarily "under the hood" and that the move won’t affect existing extensions as these can be converted into a format that can be used by Chromium-based Opera. The company is however silent whether this will affect the dozens of other Opera features which are unique to the browser. Features like Mail, RSS reader, Speed Dial, Turbo compression, Mouse gestures, Tab grouping and hundreds of nifty tricks that makes Opera stand apart from the rest of the flock.
As a long time Opera user I’m both elated and apprehensive of the direction Opera is taking. Embracing WebKit would greatly enhance website compatibility, but I’m not sure whether it justifies sacrificing a 20-year old rendering engine and all the features it supports.
The first product using WebKit will be for Smartphones, which we'll demonstrate at Mobile World Congress in Barcelona at the end of the month. Opera Desktop and other products will transition later.