I don't agree with your statement. Apps can use some low-level calls to the OS, to do things that cannot be replicated in the same way in a sandbox. So it is n

I don't agree with your statement. Apps can use some low-level calls to the OS, to do things that cannot be replicated in the same way in a sandbox. So it is not surprising that some parts of apps must be rewritten. If they are not rewritten, they just don't work in the sandbox. That's exactly the goal of a sandbox. Provide safe API for applications, and block apps that are trying to access more.