Remember the Computer Science Past Or Be Condemned To Repeat It?
Something like GDG would have been anathema to the original file system creators of Unix - at least through the Berkeley FFS days. I think I saw something like it on some extensions in 4.1ES. It was certainly on VMS. Maybe something like ext3cow will do what you are thinking of.
Of course much of the problem is that Unix at the mothership was used extensively to submit JCL to OS/360 hosts, so all that stuff was done back on the big iron, not the cheap Unix FEs. Departments had to cough up for the unix hosts but projects paid for time on big iron. I never worked on projects that cared about that - network design not legacy OSS dev.
Why The Dinosaurs Won't Die
So you are postulating the end of market economies in 10 years? Hardly likely. Face it, when the demand for those skills starts pushing pay up above other technical job types these older environments get a influx of people who went and learned it.
In any case the development environment for these systems has changed significantly. You don't submit card decks and get a print out to sift through. IDEs (Integrated Development Environments) grew in Mainframe shops, not the PC world. In many cases you can't even tell where the real work is being done unless you rip off the covers and go hunting. "Test" and "Production" environments are set up by the operations group. Development is done quite far away from there...