Not as strange as you think, perhaps. The KDE stack includes a component model called KParts, and embedding KHTML was always done via a KPart; this later allowe

Not as strange as you think, perhaps. The KDE stack includes a component model called KParts, and embedding KHTML was always done via a KPart; this later allowed a WebKit KPart to co-exist. And in fact, there once was a working KPart to embed Gecko. It didn't really see widespread use, since Gecko wasn't all that attractive in the time frame. If Servo continues to thrive, I'd be more surprised if no one attempts this. The current state of browser engine embedding in Qt/KDE also isn't too rosy. Qt switched from wrapping WebKit to wrapping Blink, and the new wrapper is currently very skimpy on extension points, making it hard or impossible to put e.g. KDE's I/O stack (HTTP, SSL, cookies, etc.) between the renderer and the web. That's a level of integration both KHTML and the WebKit KPart did allow, so things have currently regressed a fair bit. I'm not familiar with the CEF API, but it might actually allow more than Qt WebEngine (currently) does.