Keep in mind Apple has allowed third party defaults in the form of the keyboard. And yet it's not perfect. For example, when the App Store forces me to input my password (an annoying "security" feature because Apple once again thinks we're all children), it brings up the iOS keyboard instead of the keyboard default I set (Swype). This is also a security feature because of risk of keystroke logging.
So even if Apple allows defaults for other things, who knows how it'll be hampered by what Apple calls security. Or what I call Apple babying its users.
So even if Apple allows defaults for other things, who knows how it'll be hampered by what Apple calls security. Or what I call Apple babying its users.