Can anyone explain why is Apple so opposed to having different browser engineson iOS? Is it really just about security? I don't understand what is Apple to gain by not allowing 3rd party engines everywhere in the world.
And of course they want to do that. What is good for the web is bad for Apple. They need web apps to be unviable to maximise the platform lock-in and the rents they can extract via the App Store.
("They" being senior Apple leadership; I'm sure the people working directly on WebKit are doing the best they can given their resource constraints and strategic guidance.)