It's not gray. Your examples do not violate policy because Apple has an explicit exception to allow stuff like that when specifically running in WebKit's JavaScript engine. That's why they use JavaScript, to qualify for the loophole. But as I said, Roblox does not use JavaScript or WebKit for running games and does not qualify for that exception. There is also an exception for "plug-ins" which seems like it could cover the case of camera filters, but definitely would not stretch to cover an entire embedded app store full of complete games purchased with a third-party currency.