Why would Apple ever want to replace the engine they develop? I'm not sure that's been considered a priority, or even an option. However, they do release WebKi

Why would Apple ever want to replace the engine they develop? I'm not sure that's been considered a priority, or even an option. However, they do release WebKit for use by others, so in that sense I presume there's a certain looseness in the coupling. Which is not to say there aren't assumptions that will have to be unwound.