I agree, but I’m slightly more hopeful that someone could still take KHTML (again) and take it into the mainstream (again). At the end of the day, there isn’t that much extra functionality in browsers these days, most features are in the core engines (html and js). If anything, browsers have actually lost functionality (with fewer skinning and extensibility options, less emphasis on integrated services like bittorrent or ftp, no desktop integration, etc).

So yeah, we wouldn’t get a new browser engine, but I think a new “fully featured” browser imho is possible. Vivaldi for example, while built on Chromium, is substantially different in terms of features.