Stock apps are part of the core build and can't be physically deleted. Removing them from the home screen merely hides them and deletes the associated user data. You can restore them again from the App Store, but this is merely a convenience used because that's where people expect to find apps. The mechanism behind the scenes is different than for a third-party app, however. Nothing is really downloaded, so it's instantaneous. The app is merely unhidden again.
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After a restart, you always need to use your passcode. There needs to be some way to unwrap your encryption key from the secure enclave. However, thereafter, Touch ID works for app purchase and has done so since iOS 9 (as has the ability to turn off the need for a passcode for free apps).
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In keynote, they said July.