File permissions are completely insufficient to achieve the kind of design that PipeWire is aiming for. None of the problems outlined in the article regarding PulseAudio (e.g. the ability of applications to interfere or snoop on each other, or requesting code being loaded into a shared address space that have unlimited access) can be easily handled with file permissions at all. The model is simply not expressive enough; no amount of hand-wringing about context switching will change that. This is one of the first things addressed in the article and it's very simple to see how file permissions aren't good enough to solve it.