I don't see how this is relevant. Nobody is advocating for the relaxations of the iOS security model itself, which is the actual thing that prevents rootkits and malware on your device.

Instead, the proposal is that people be able to install whatever software they want, that runs as a normal iOS app subject to the iOS security restrictions. Being able to install a non-Apple-approved app does not give you the ability to read and write arbitrary kernel memory, or do other actually dangerous things.