"Marble Madness" is a good one, you can discuss the unreleased "Marble Man" sequel which was rediscovered years later and is widely emulated using Mame. An of course the then 18yo author of Marble Madness, Mark Cerney is a living video games legend designing games such as "Sonic the Hedgehog 2", "Crash Bandcoot", "Spyro the Dragon", "Uncharted, "Ratchet and Clank", "Knack" and lots more

There are also numerous other webpages saying that the guy who owns 2 different types of the original machine (one with joysticks / one with trackballs) won't part with the ROMs unless people pay $50,000...

Seems so. I was sure that this game was one of those that around about 2003 being a very limited hardware architecture started a flurry of Mame activity. Perhaps the ROM was given to them and the driver written but the ROM never leaked.