It probably wouldn't be legal for Apple to cripple non-App Store apps like that.If this passes, be prepared for serious limitations/costs on the use of Apple's SDK. Apple owns their system. There will always be restrictions put upon developers to access it.
People are constantly suggesting "clever" loopholes for Apple to defeat antitrust legislation without realizing that Apple is already taking this incredibly immature approach in South Korea and the Netherlands, and the response from regulators hasn't been "Oh, gee Apple, you got us! I guess we can't do anything then."