Isn't that basically what OS X app sandboxing is? Well, the results of Open File aren't an opaque blob, but the app doesn't have permission to access files outs

Isn't that basically what OS X app sandboxing is? Well, the results of Open File aren't an opaque blob, but the app doesn't have permission to access files outside its sandbox until the user uses the Open dialog, which grants the app access to the file in question.