Yep, that's pretty much what I've described, and it is the reason why I'm certain that there's no technical limitation at play here. Apple just chose to not allow this for political/strategic reasons.

Which is fine if you're doing an HTML UI (PhoneGap) since the DOM and JS engine share the same process. If you're doing a native UI with JS then it must marshal cross process to affect the UI then you have to decide which is worse, no JIT or cross process overhead.