What you are doing is adding an extra dimension to your permissions vector, instead of just worrying about which users can access what you have to think about i

What you are doing is adding an extra dimension to your permissions vector, instead of just worrying about which users can access what you have to think about individual programs. There are already implementations of this, for example SELinux. It difficulties in that how do I know which files a particular program might need and how is this implemented at a UI level? For example, what if a program asks for permissions on PNG files? Is this because it wants to manipulate them or is it simply that some of it's internal assets are stored as PNGs? What happens if I add a plugin or update to a program that allows it to work with different file types? How do you prevent "dick moves" like a new program locking other programs out of a file type it decides to claim? How do you implement the UI? Is it some central permissions manager or do you have endless popups (which people are likely to just unthinkingly click accept on)?