Anyone remember an IE GUI called IEOpera that tried to mimic Opera's GUI on the IE engine? Opera's lawyers objected, so it became Avant Browser instead. The irony is that Opera is now going to become a GUI for Webkit.
A rendering engine is more than just how a browser lays out a page. It defines the character of the browser itself. The way Opera instantly reflows pages accurately when you toggle the side bar or zoom is all part of the rendering engine (one of the reasons I always preferred it over clunky IE, and even Firefox on slower machines years ago). Many of the things Opera allows or does better than rivals are down to the architecture of its own rendering engine too. Not everything will be transferable to Webkit. Other things will be copied but won't work quite the same way.
And where does this leave Opera's additional components such as IRC, email, RSS etc? Will they either completely change or be dropped like some other features have been recently?
Switching to Webkit is more than just changing rendering engines. It's going to be the end of Opera as we know it. I'm sure someone will argue about market shares and compatibility etc, but that's no comfort to existing long term users who have chosen it for the way it feels and behaves.
Given the trend over the last decade to follow standards and the cooperation of browser vendors in creating HTML5, I doubt whether this is really about compatibility. Opera weathered that problem right through the original browser wars over three rendering engines. The current browser war has been about implementing HTML5 and speeding things up, and Opera has kept up there too. I think this is really about making the company leaner and more profitable by reducing staff and the costs of maintaining Presto. Realistically, what are they going to make the core devs do instead over the next 10 years? hey'll be eased out through natural wastage or redundancies in due course. Given how the mail and chat clients have always hobbled along on a shoestring budget, I doubt they'll suddenly pour resources into them. Mail is no longer important to Opera as it was in the days before social networking.
So, it's a shame but it doesn't surprise me much. From the moment Jon von Tetzchner was ousted by the board, the Opera of old was on borrowed time, both as a company and a browser.
Is any of Chrome not open source? If Opera use an OS engine but proprietary browser shell, that's going to give another angle for its closed source bashers.