> There's no way z/OS is going to be free or open-source (if for no other reason than if they open sourced it, you'd still need a mainframe, which means you're going to pay IBM for cloud time)
This is probably why IBM mainframe OSes until the 1980s are public domain: You can't run MVS without an IBM mainframe, so why bother even copyrighting the source code? The Hercules people are grateful for that bit of pragmatism.
http://www.hercules-390.org/hercfaq.html