My feeling is that the game should end on a random year between around 2050 and 2500, with the actual end date changing from game to game. This way, people would be kept on their toes, as they wouldn't know EXACTLY when the game was going to end!!! They couldn't, for example, throw their reputation to the wind so as to win the domination victory in the next 8 turns!
Also, rather than 'extraplolate' I think it would be easier to retain future techs but, as I have said previously, give them in-game benefits to such things as unit strengths, production, commerce, population growth and the like!
Lastly, rather than a 'mission to AC', I would rather see the Space Race mission be about a more gradual accumulation of points-garnered from a variety of successful missions-be they sattelite launches, exploration missions, space stations or off-world colonies.
Yours,
Aussie_Lurker.