Future techs may not be what civ is about, but future civ could include future techs. In my opinion, if Civ is about anything beyond just fun then it is about the impact of technological progress on history, and extending it into the future is reasonable. However, near future tech should be based on realistic projections of near future technology, the stuff futurists are really talking about, while far out stuff should be reserved for the distant future. Next War is not the right answer.
Ideally, this would go along with a more unpredictable research system. Research leaps on the level of civ Techs are basic scientific discoveries, not mere engineering that you can order developwed. A ruler might order that research be conducted based on a particular known tech, but would not be able to predictate which as yet unknown tech was to be found. Thus, if you had pottery it might lead to bronze working (what are these shiny rock residues in the kilns?) or to writing (we can put stylized picture labels on the pots by scratching the clay!) or to wine making or masonry. You don't know what you will get, just that you want your people to focus more on pottery and less on fishing. As a game some strategic plan gaming might be lost, but perhaps more directable engineering type techs could be necessary after basic research type techs. Thus, futures that differ from our own might be explicable as diffrent random breakthroughs, as long as the major likely paths are judiciously included.
If this is done, there should be opportunities to win in every era, perhaps one new victory coming into play in each period, and some perhaps being ruled out. In my FutureMod I include the UN and Diplomatic victory, but once you enter the future era and discover Utopianism it obsoletes the UN. So there's a window during which that victory condition is achievable. Thus the game is winable yet concievably indefinite. No "OK, its 2050, time to add up points."
The problem with going too far into the future with Civ is that it doesn't do space very well, and space is inevitably a part of the future. If its not there, you wonder why not. In order to do space, civ would have to do spherical worlds, and the way to get that is with what I call diagonal wrap: the map is square and two oppsite corners are poles. Points on edges adjacent to the same pole wrap to each other backwards. Also you would need multiple maps, representing different planets, and a main solar system map on which all objects such as planets and spaceships move in circular paths depending on distance from the sun and accelerate and where spaceships can go to and from the planets, thus moving to different maps.
Incidently, in my FutureMod for BtS I made a time travel reciever building that allows units from the future to appear occiasionally (and randomly, beyond your control). At the very end of the game you can make a time travel transmitter.
