Such a weird statement. webkit is and has been a fully released browser engine for decades, companies forked from it for licensing and profit, not because it wasnt ready or complete (at the time)
Same as any browser engine, there isn't a new engine since 20 years. Apart of Gecko, Blink and WebKit there are nothing else, apart of some experimental ones, mostly discontinued.
WebKit is a fork from KHTML (KDE) and Blink is an improved fork from WebKit.