If Linux was on the tech tree, only the civilizations who researched Linux could use it. That’s not very FOSS! Every civilization who had computers should be able to get Linux once it’s out.
Actually that would be an interesting mechanic: to move forward in the tech tree you have to research something, but by researching it you give it all the players.
Do you stall your own progress, or take the hit to move forward and float all ships higher by raising the technological tide? How do the devs program the AI countries to make choice(s) in single-player, and what would a human player do?
Who blinks first?
This exists in other 4X games but not really any of the Civ series IIRC. You can trade generic science points but certain technologies and civics could be shared directly by trade and military engagements with foreign powers (wheel, military tactics, currency, printing press, etc).
