Completely unscientifically asking here-- what would be a fair amount of time for a game to exist before entering the public domain; just your gut reaction? 30 years? 35?
I think 20 would be "a good start" right now, but it's probably too short for the long term, especially as technological advances slow down and the innovation curve flattens out. I remember when 30FPS at 1080p resolution was really something special, but it's a minimum spec since the Xbox 360 in 2005 -- 14 years ago.
30 years ago -- still commercially viable, but just barely. It's a very long time ago. I'd say public domain them, but allow exceptions IF someone like Nintendo wants to monetize A FEW of them in a consumer-friendly way.
Golden Axe, Stun Runner, Super Mario Land, TMNT NES, Phantasy Star II, SimCity, Shadow of the Beast, Dragon Warrior, Populous, Harpoon
35 years ago -- yeah, these and things that came before them should be in public domain for sure.
Pac-Land, Grobda, Super Xevious, Hydlide, Infocom text games, King's Quest, Impossible Mission, Donkey Kong 3 NES, Pitfall II Lost Caverns, Gateway to Apshai. Discontinued: Atari 5200, Odyssey 2, Vectrex.