Let me say this up front: I don’t know what Opera has up its sleeve. I’m sure you’ve heard some things. But it’s not hard to find people who think everyone — meaning Opera, Microsoft, and Mozilla — should switch to WebKit. In WebKitopia, the thinking goes, we’d have One True Browser Core that magically banished incompatibilities forever.
Except it wouldn’t. Business competitiveness and user fragmentation would ensure as much.
As Peter-Paul Koch explained back in 2009, There is no WebKit on Mobile.
There’s not really a WebKit on desktop either. On desktop, there’s Apple’s Safari, which uses WebKit’s JavaScriptCore, and Google’s Chromium / Chrome which uses V8. Google developed V8 for speed. If Opera was so inclined — and I can’t emphasize enough that this is a hypothetical scenario — they could release a version of WebKit’s rendering core with Carakan as the JavaScript engine.
WebKit, as a project, is dominated by employees of Apple and Google. Those companies can easily prevent a feature from gaining traction. A feature could, for example, land in core, but take some time to be released in a product. Or a feature can be committed to Safari, Chromium, or some other fork without making it back into WebKit core at all. (This is probably a good time to mention that Chromium says it prefer[s] to contribute as much code as possible upstream to improve all WebKit-based browsers.
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And this is before we discuss mobile device implementations. Android WebKit (which is essentially dead, but still lives on in older Android devices) is different from iOS Safari, which is different from Chrome for Android, which is different from BlackBerry’s WebKit, and Ericsson’s experimental Bowser.
If this sounds at all like fragmentation, it should. That’s exactly what it is. WebKit is not a cure-all for what ails us.