I would love to see tech diffusion added to CCTP. Right now in my main CCTP game, it's 1992, I'm in the modern era, and some of the civs are still in the Renaissance or Industrial eras, which because I am in the modern era and trading with a lot of civs, it doesn't make a whole lot of sense for me to completely dominate everyone technologically. Especially once Radio/Internet is researched. Maybe have it so that radio/Internet gives a huge bonus in science when researching a tech another civ has already discovered? And maybe trade routes could give a higher science boost if the civ you're trading with has significantly less advanced technology.
Also, this is merely a cosmetic issue than anything, but the current tech tree makes me research items about 50-100 years later than they have been in real life, and I have the most advanced empire in the game.