They locked out access to anything but /Data, /opt0, /opt1, a: and b:.
My wife was already chasing me to "simplify" the filesystem so she could find things she actually cared about. Perhaps someone's wife at Sony was making the same suggestion.
They also slightly modified the file format for the media.xml files. Which is a possible issue for prs500 but not for my code (as it doesn't touch those files, yet...)