A better use for Hercules
The discussion about what to run on Hercules (or any other z/Series emulator) has missed one particularly useful environment - application development. Until recently, IBM offered a Flex-ES based system with a specially licensed z/OS bundle known by the catchy abbreviation ADCD (Application Development CD, which was really a DVD). If I recall correctly, this package carried a price tag of about $20,000 - not cheap but not hugely expensive. This was not intended to replace a production mainframe, but to provide an environment for developing and testing application software.
IBM and Fundamental (the developer of Flex-ES) have apparently had a falling out of some sort. It seems to me, however, that Hercules would be an ideal platform for the ADCD.
PS: I believe you can legally run MVS 3.8j on Herc, but that is a very aged OS, too