I'm not seeing how this would be used. You'd have a module used by Perl programs that would presumably have those programs writing to this virtual disk (virtual file system). Question #1: How will you synchronize all this virtual file system activity across those programs? Question #2: What does this data end up looking like on the real disk? Eventually you have to write it out somewhere. Question #3: How will non-Perl programs accessing the same files be managed?

Maybe some proposed examples of usage would clear some of that up. Me thinks you may be trying to reinvent a much bigger wheel than you realize. There's a reason filesystems are implemented in OS kernels.

If your idea is really to have a filter for data coming from and going to the real filesystem for some sort of consistent Perl view of the world, I'd look at writing a file handle tie module.