PLATO was a very interesting system that isn't as well known as it should be.
Sadly it's still in copyright/IP lockdown, even though most of the system was presumably developed by the University of Illinois and the largely defunct CDC. As a result the software is unavailable for emulation or study.
What would happen if we decided to completely ignore these claims for this, which seems to be abandonware. Who would come after us? Could we claim fair use if we are attempting to reconstruct work and social interactions of the past, not unlike a renaissance fair or a historic battle reenactment?
The IP from CDC must have passed down to whatever companies purchased the company. I bet Illinois would slap down people also - nothing a university likes more than asserting their IP.
I'd imagine the problem is more about obtaining documentation, ROMs, OS files etc. Emulators of questionable legality have always been around, for platforms more commercially interesting than this. But it's rarely lead to legal action.
There is some risk. Until someone proves ownership of the IP, nobody large enough to be worth suing can safely do it. The organisation who operates the emulator has a license.
